World Health Organization SAGO, "Independent assessment of the origins of SARS-CoV-2" (June 27, 2025)
Summary
A report dated 27 June 2025 from the Scientific Advisory Group for the Origins of Novel Pathogens (SAGO) to the WHO Director-General assessing the origins of SARS-CoV-2. Its executive summary says most available published scientific evidence supports zoonotic transmission from animals, possibly from bats or an intermediate host, but that SAGO is not currently able to conclude exactly when, where and how the virus first entered the human population. It reports no scientific evidence supporting deliberate manipulation of the virus in a laboratory and no additional evidence for introduction through frozen products at the Huanan Seafood Market. SAGO states it did not have access to original raw data and that information sought from the Governments of China, Germany and the United States of America had not all been provided.
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Scientific Advisory Group for the Origins of
Novel Pathogens (SAGO)
Independent assessment of the origins of
SARS-CoV-2
Publication Date 27 June 2025
2
© World Health Organization 2025
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SARS-CoV-2 from the Scientific Advisory Group for the Origins of Novel Pathogens (SAGO). Geneva,
Switzerland. Available at: https://bit.ly/SAGO-SARS-CoV-2
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Table of Contents
Authors................................................................................................................................................ 5
Acknowledgements ............................................................................................................................. 7
List of abbreviations ........................................................................................................................... 7
Executive summary............................................................................................................................. 8
Background ..................................................................................................................................... 13
Aim of SAGO’s independent assessment of the origins of SARS-CoV-2 ................................... 16
Methods............................................................................................................................................ 17
Results .............................................................................................................................................. 20
Early investigations and human cases ........................................................................................... 20
Testing for SARS-CoV-2 in animals and the environment at the Huanan Seafood Market ......... 26
Detection of SARS-CoV-2 in wild animals in China and South-East Asia .................................. 28
Animal infection experiments and reverse zoonoses .................................................................... 32
Environmental investigations ........................................................................................................ 34
Genomic Investigations................................................................................................................. 34
Biosafety & Biosecurity Investigations ........................................................................................ 38
SAGO’s Evaluation of other reports on the hypotheses of the origins of SARS-CoV-2 spillover into
the human population ........................................................................................................................ 41
Published Scientific Reports (Summarised in Table 3.A) ............................................................ 41
Intelligence Reports/Reports from Governments (Summarised in Table 3.B) ............................. 43
Discussion ............................................................................................................................................ 53
Conclusion ........................................................................................................................................... 57
References ............................................................................................................................................ 62
Annexes ................................................................................................................................................ 72
Annex 1. Table 1. Animal species naturally infected (RNA detection) by SARS-CoV-2.......... 72
Annex 1. Table 2. Animal species susceptibility to SARS-CoV-2 based on experimental
infection studies ............................................................................................................................... 76
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The following members of the Scientific Advisory Group for the Origins of Novel
Pathogens (SAGO) authored this report to the WHO Director-General
Authors
Chairs
Marietjie Venter, Chair of the SAGO; Distinguished Professor and Research Chair: One Health
Surveillance and Vaccines at the University of the Witwatersrand, Johannesburg, South Africa
Jean-Claude Manuguerra, Vice-Chair of the SAGO; Professor and Director of the Environment and
Infectious Risks Unit, Institut Pasteur, France
Members
Phillip Alviola, Associate Professor at the Animal Biology Division, Institute of Biological Sciences,
University of the Philippines, Philippines
Abdullah Assiri, Assistant Deputy Minister for Preventive Health, Ministry of Health, Saudi Arabia
Stuart D Blacksell, Professor of Tropical Microbiology, Centre for Tropical Medicine and Global
Health, Nuffield Department of Medicine, University of Oxford, United Kingdom of Great Britain
and Northern Ireland
Inger K Damon, Adjunct Professor of Clinical Medicine, Emory University, Atlanta, United States of
America
Christian Drosten, Professor and Head of the Institute of Virology, Charité Medical Center, Germany
Elmoubasher Farag, Clinical Associate Professor, Vice President for Medical and Health Sciences
Office, Qatar University, Doha, Qatar
Thea Kølsen Fischer, Professor of Public Health, Virus Infections and Epidemics, University of
Copenhagen, Denmark and Director of Research & Innovation, Nordsjællands Hospital, Hillerød,
Denmark
Raman Gangakhedkar, Distinguished Professor, Faculty of Medical & Health Sciences, Symbiosis
International University, Pune, India
Nada Ghosn, Head of the Epidemiology Surveillance Program and Medical officer, Directorate of
Prevention at the Ministry of Health, Lebanon
Maria Guzman, Head of the Center for Research, Diagnostic and Reference of the Institute of
Tropical Medicine, Pedro Kouri, Cuba
Christian Happi, Professor and Director, African Center of Excellence for Genomics of Infectious
Disease, Redeemer's University, Ede, Nigeria
Gladys Kalema-Zikusoka, Founder and Chief Executive Officer of Conservation Through Public
Health, a nongovernmental organization in Uganda
Normand Labbe, biosafety inspector, Public Health Agency of Canada, Canada
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Authors1 (continued)
Khin Myint, Scientific Advisor, Exeins Health Initiative, Jakarta, Indonesia
Hung Nguyen-Viet, Program Leader (a.i.) of Health, International Livestock Research Institute,
Kenya
Chinwe Lucia Ochu, Director, Planning, Research and Statistics, Nigeria Centre for Disease Control,
Nigeria
Masayuki Saijo, Director General for the Medical Affairs and Public Health, Sapporo City Health and
Welfare Bureau, Sapporo, Japan
Rosemary Sang, Advisor and Chief Research Officer, Centre for Virus Research, Kenya Medical
Research Institute, Kenya
Kathrina Summermatter, Head of the Biosafety Center and Managing Director of the Biosafety Level
3 Laboratory at the Institute for Infectious Diseases, University of Bern, Switzerland
Supaporn Wacharapluesadee, Senior Researcher, Thai Red Cross Emerging Infectious Diseases
Clinical Center, King Chulalongkorn Memorial Hospital and Chulalongkorn University, Thailand
John Watson, Visiting Professor, Research Department of Infection and Population Health, University
College, London, United Kingdom of Great Britain and Northern Ireland.
1
Three SAGO members; Yungui Yang, Deputy Director, Beijing Institute of Genomics, Chinese Academy of
Sciences, China, Vladimir Dedkov, Deputy Director for Research, Pasteur Institute, Russian Federation, and
Sowath Ly, Deputy Head of Epidemiology and Public Health Unit, Institut Pasteur du Cambodge, Cambodia,
requested to not be listed as authors of this report. Carlos Morel, who was previously a SAGO member, also
asked for his name not to be listed as an author and resigned from SAGO on 13 June 2025.
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Acknowledgements
SAGO and WHO extend their gratitude to all who presented to SAGO, including the Chinese Center
for Disease Control and Prevention; Beijing Institute of Genomics, Chinese Academy of Sciences;
National Health Commission of the People’s Republic of China; Institute of Pathogen Biology,
Chinese Academy of Medical Sciences; University of Arizona; University of California, San Diego;
Technical University of Denmark, and the University of Sydney, Australia. WHO wishes to thank all
who have conducted research to find the origins for COVID-19 and shared their findings, and more
broadly to those who have kept the pursuit scientific and factual. WHO also wishes to thank its
partner organizations FAO and WOAH for their support as observers of SAGO.
List of abbreviations
APHIS Animal and Plant Health Inspection Service
BSL biosafety level
CDC Center for Disease Control
CLIA Chemiluminescence immunoassay
CNIC Chinese National Influenza Center
CoV Coronavirus
COVID-19 Coronavirus disease 2019
eCLIA Electrochemiluminescence immunoassay
ELISA Enzyme-linked immunosorbent assay
FCS Furin cleavage site
GISAID Global Initiative on Sharing All Influenza Data
HSM (also known as Huanan Seafood Wholesale Market, or Wuhan
HSM Wet Market)
ILI Influenza-like illness
MERS Middle East Respiratory Syndrome
NGS Next generation sequencing
NHC National Health Commission
NIC National Intelligence Council
ODNI Office of the Director of National Intelligence
PCR Polymerase chain reaction
PPE Personal Protective Equipment
RDB Receptor-binding domain
RDT Rapid diagnostic test
RT-PCR Reverse Transcriptase PRC
SAGO Scientific Advisory Group for the Origins of novel pathogens
SAR Special administrative region
SARS-CoV-2 Coronavirus causing COVID-19
SNV Single nucleotide variant
SSCP Select Subcommittee on the coronavirus pandemic
USA United States of America
USD United States Dollars
VNT Virus neutralization test
WHO World Health Organization
WIV Wuhan Institute of Virology
WOAH World Organisation for Animal Health
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Executive summary
The COVID-19 pandemic, caused by the severe acute respiratory syndrome coronavirus 2
(SARS-CoV-2), has been one of the most severe health crises in the past century. Between December
2019, when the first cases of pneumonia of unknown etiology were reported from Wuhan, China, and
May 2023, when the Director-General of the World Health Organization (WHO) declared that COVID-
19 was no longer a public health emergency of international concern, more than 7 million deaths were
reported to WHO. However, WHO estimates the true toll of the pandemic to be at least 20 million lives
lost based on the excess deaths estimated in countries around the world. Underreporting of deaths
directly attributed to COVID-19 because of pressure on healthcare systems during the pandemic, limited
diagnostic testing, and deaths indirectly associated with COVID-19 contribute to the underestimation
of reported deaths. The pandemic also caused severe disruption to societies and livelihoods (WHO,
2023a), with economic losses estimated to be at least USD 11–16 trillion, (GPMB, 2020) (Cutler and
Summers, 2020).
In May 2020, the 73rd World Health Assembly adopted resolution 73.1 calling for a One Health
approach to identify the source of SARS-CoV-2 introduction into the human population (WHO, 2020d).
To date, there have been three scientific missions to China, with one specifically focusing on
understanding the origins of COVID-19 in February 2021. In November 2021, the WHO Director
General established the Scientific Advisory Group for the Origins of Novel Pathogens (SAGO) — a
group of 27 independent international scientific experts — acting as an advisory board to WHO in this
field; tasked with designing a framework to investigate the origins of emerging and re-emerging
pathogens and to evaluate scientific evidence to determine the origins of SARS-CoV-2 (WHO, 2021a).
This is not solely a scientific endeavour it is a moral and ethical imperative. Understanding the origins
of SARS-CoV-2 and how it sparked a pandemic is needed to help prevent future pandemics, save lives
and livelihoods, and reduce global suffering. Ultimately, this pursuit underscores our collective
responsibility to safeguard human health and well-being.
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Despite the vast amount of research on SARS-CoV-2 and our increased understanding of its evolution
and epidemiology, reports by scientists and governmental agencies have provided opposing views as to
the virus’ origins, without clear conclusions, and often without presenting the data underpinning those
views.
SAGO provided initial findings and recommendations to better understand the origins of SARS-CoV-2
in a report published on 9 June 2022 (WHO, 2022). This current review updates its evaluation based on
information from published scientific papers and reports, available intelligence statements and reports,
scientific presentations provided to SAGO and expert discussions held by SAGO during closed
meetings between November 2021 and June 2025.
It is important to note that SAGO did not have access to original raw data from any source in preparing
this report. SAGO and WHO have requested further information from Member States, - including the
Governments of China, Germany and the United States of America. Information was sought to clarify
critical unknowns following the publication of the WHO-China March 2021 report and SAGO 2022
report, as well as data used to generate government reports. However, at the time of writing, all of the
required information had not been provided to WHO. The focus of deliberations in this SAGO report
is therefore predominantly based on available peer-reviewed scientific data. SAGO also reviewed
preprint materials and private/government reports for any additional data, scientific information that
could be used to better understand different hypotheses on the origins of SARS-CoV-2.
SAGO continues to articulate areas where the group feels scientific data is sparse, and what studies are
needed to address limitations in our understanding of the origins of this pandemic. There have been
several hypotheses proposed on the origins of SARS-CoV-2, some which had been discussed in the
WHO-China 2021 mission report (WHO, 2021c) and further investigated in the SAGO preliminary
report (SAGO, 2022).
SAGO evaluated the currently available scientific evidence that may support or dismiss these
hypotheses in this report.
Hypotheses include:
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1) introduction from a natural zoonotic source(s) as a spillover event(s) either directly to humans
from wild animals or through an intermediate host;
2) an accidental laboratory-related event, which may have involved exposure to the virus during
field research or a breach in laboratory biosafety procedures;
3) an introduction of SARS-CoV-2 into animal markets via cold chain processes and subsequent
infection in humans through contact with products sold at markets, and
4) deliberate manipulation of the virus in a laboratory, followed by a laboratory biosafety breach.
Hypothesis #3 - an introduction of SARS-CoV-2 into animal markets in China from overseas via the
importation of products through the cold chain was evaluated in the SAGO 2022 report (WHO, 2022).
No additional evidence to support this hypothesis has become available to suggest that transmission of
SARS-CoV-2 to humans from frozen products at the Huanan Seafood Market (HSM) or any other
market in Wuhan occurred. SAGO will re-evaluate this hypothesis should additional evidence become
available.
To evaluate hypothesis #4, of a deliberate manipulation of the virus in a laboratory and subsequent
biosafety breach, SAGO analysed the genome structure of the virus and publications and reports
addressing the likelihood of manipulation through reverse-genetics but did not find scientific evidence
supporting this hypothesis over evidence that these mutations and recombination events also occur in
coronaviruses in nature. This hypothesis also remains largely unsupported by other scientific and
intelligence reports. SAGO will re-evaluate this hypothesis should additional evidence become
available.
This report will focus on the two main hypotheses. While most available and accessible published
scientific evidence supports hypothesis #1, zoonotic transmission from animals, possibly from bats or
an intermediate host to humans, SAGO is not currently able to conclude exactly when, where and how
SARS-CoV-2 first entered the human population. The closest known precursor strains were identified
in bats in China (2013) and the Lao People’s Democratic Republic (2020); however these strains are
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too distantly related to SARS-CoV-2 to be the direct source of the COVID-19 pandemic. While
available data support that the HSM played a significant role in early transmission and amplification, it
is not conclusive that the HSM was where the virus first spilled over into the human population, or if it
occurred through upstream infected humans or animals at the market. Metagenomic evidence identified
several species of wildlife that were sold at the HSM in Wuhan, China, that should be investigated as
potential intermediate hosts that may have infected early human cases. Currently, evidence needed to
confirm this hypothesis is lacking, including comprehensive upstream investigations into wildlife
species raised, traded and sold at the HSM and in other markets in and around Wuhan. This is needed
to fully understand where, when and how the earliest humans were infected, which intermediate host(s)
species were involved, and the conditions in which transmission(s) occurred leading to the earliest
human cases.
Much of the information needed to assess hypothesis #2, of an accidental laboratory related event, either
during field investigations or a breach in laboratory biosafety or biosecurity, has not been made
available to WHO or SAGO. WHO has made several requests to the Government of China to provide
health records of staff and documentation on biosafety and biosecurity practices and procedures in
laboratories in Wuhan, including the Wuhan Institute of Virology (WIV) and the Chinese Centers for
Disease Control in Wuhan as recommended in the 2022 SAGO Preliminary Report (SAGO, 2022).
Without information to fully assess the nature of the work on coronaviruses in Wuhan laboratories, nor
information about the conditions under which this work was done, it is not possible for SAGO to assess
whether the first human infection(s) may have resulted due to a research related event or breach in
laboratory biosafety. It can therefore not be ruled out, nor can it be proven until more information is
provided.
SAGO reiterates its request to all governments — especially those where the earliest human cases were
confirmed— to share information, data, and findings from investigations of the earliest human cases,
interventions and testing in markets and sites of animal breeding including husbandry of captive
wildlife, as well as any potential research-related accidents or breaches in biosafety including evidence
regarding studies that may have involved culture and/or research on immediate genetic precursors to
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SARS-CoV-2 in the laboratory. SAGO likewise reiterates its request for any researchers, scientists or
governments with information on the origins of SARS-CoV-2 to make it available to WHO and SAGO.
The work to understand the origins of SARS-CoV-2 remains unfinished.
To conclude, while a zoonotic origin with spillover from animals to humans is currently considered the
best supported hypothesis by the available scientific data, until requests for further information are met
or more scientific data becomes available, the origins of SARS-CoV-2 and how it entered the human
population will remain inconclusive.
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Background
More than five and a half years have passed since December 2019, when the initial human cases of a
novel coronavirus, later named SARS-CoV-2, were reported in Wuhan, China. This marked the
beginning of the most significant pandemic of this century. SARS-CoV-2 has infected billions of people
globally and significantly affected all countries, communities and families. While reported deaths
exceed 7 million (WHO, 2025), the actual number of deaths is estimated to range from 14.9 million
(WHO, 2023a) to more than 18 million (Wang et al., 2022) by the end of 2021, based on various
estimates of excess mortality studies during the initial years of the pandemic. Despite vast amounts of
research conducted on this virus, the definitive route through which it entered the human population
remains unknown. A deeper understanding of this emergence is crucial for mitigating future pandemics.
On 31 December 2019, the WHO China Country Office was informed of cases of pneumonia of
unknown etiology detected in Wuhan City, Hubei Province, China (WHO, 2020c). Genetic sequencing
and phylogenetic analyses of samples taken from early cases indicated that the virus belonged to the
coronavirus family, specifically the Betacoronavirus 2B lineage within the Sarbecovirus subgenus. The
virus first became known as ‘2019 novel coronavirus’ (2019-nCoV) and was later named SARS-CoV-2
by the International Committee on Taxonomy of Viruses (Gorbalenya et al., 2020). While it is
understood that partial and potentially full sequences may have been available in December 2019 and
early January, the first full genome was made publicly available on 11 January 2020 (China National
Center for Bioinformation, 2022). The closest related viruses to this novel coronavirus at the time was
the known bat SARS-like coronavirus RaTG13 with a 96.1% genomic similarity, collected in China in
2013 (Zhou et al., 2020b), as well as Banal-52 (96.8% homology) collected in Lao People’s Democratic
Republic in 2018, and the sequence later reported (Temmam et al., 2022). More detail on closely related
coronaviruses is provided in later sections of this report (Sections: Detection of SARS-CoV-2 in wild
animals in China and South-East Asia and genomics investigations).
An initial WHO mission team—comprised of staff from the WHO Country office in Beijing and the
Western Pacific Regional office in Manila—conducted a field visit to Wuhan from 20-21 January 2020.
The mission aimed to gather epidemiological information and to understand response actions. They
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provided their findings to WHO on a) the epidemiology of the outbreak known at the time, b) case
definitions used by Chinese authorities, c) case management of patients, d) infection prevention and
control in health facilities, and e) risk communication by Chinese officials, among other topics (WHO,
2020b).
From 16-24 February 2020, WHO and Chinese representatives conducted the first international joint
mission to China (WHO, 2021c). The team included 25 national and international experts from China,
Germany, Japan, the Republic of Korea, Nigeria, the Russian Federation, Singapore and the United
States of America (USA). During the nine-day mission, the joint international-China team met with
Chinese officials, agencies, institutions and hospitals involved in the COVID-19 response in several
Chinese cities to better understand what was known about the virus, the earliest cases and their clinical
severity, transmission dynamics of the virus, as well as prevention, control and response measures being
adopted at national and local levels. The international mission team visited several field sites, including
community centres and health clinics, county/district hospitals, designated COVID-19 hospitals,
transportation hubs (air, rail, road), a wet market outside of Wuhan, warehouses for stocks of
pharmaceuticals and personal protective equipment (PPE), research institutions, provincial health
commissions, and local Centers for Disease Control (provincial and prefecture). A subset of the mission
team also visited Wuhan, China, but their purpose was not to understand the origins of SARS-CoV-2,
but rather to see first-hand the efforts to reduce the spread, care for patients and protect health workers.
The full agenda of this mission is available in the report (WHO, 2020b).
The international team produced a report, published by WHO in February 2020 (WHO, 2020), outlining
key findings of the mission, including a) virus characteristics, b) the timeline of the outbreak in different
Chinese cities, as was known at the time, c) detailed transmission dynamics and secondary attack rates
in different settings, d) disease progression and severity, e) details of response policies and actions by
Chinese authorities, and f) critical knowledge gaps for which evidence was needed to guide prevention
and control efforts in China and globally. The report provided recommendations for China, for
countries with imported cases, for unaffected countries, for the public, and for the international
community. At the time, there were approximately 75,500 COVID-19 cases reported in China. The
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report commented on the importance of addressing knowledge related to the source of infection of the
earliest cases needed for guiding control strategies (e.g., animal origin and natural reservoir of the virus,
human-animal interface of the original event, early cases whose exposure could not be identified).
One year later, in February 2021, WHO and China organized a second international mission to China
to work with government officials, technical partners and researchers in China specifically to investigate
the origins of SARS-CoV-2. The terms of reference for this mission were agreed upon by China and
WHO in July 2020 (WHO, 2020f) and the mission included international experts from Australia,
Denmark, China, Germany, Japan, the Netherlands, the Russian Federation, Sudan, the United
Kingdom of Great Britain and Northern Ireland, Viet Nam, and the United States of America. This
mission produced a detailed report and annexes published by WHO in March 2021, which described
specific information about the earliest cases, analyses of data from various disease and mortality
surveillance systems as well as findings from early investigations that took place in China (WHO,
2021c).
The joint WHO international and China team advocated for further studies to better understand the
origins of SARS-CoV-2 and its evolution. The report provided detailed information about the
epidemiology of the earliest cases as well as data from different surveillance systems from Wuhan and
the Hubei region, details related to animal and environmental studies and findings related to molecular
epidemiology. The report concluded without being able to identify the origins of SARS-CoV-2, nor
how the pandemic began (Koopmans et al., 2021; WHO, 2021).
Recommendations from the international and Chinese team included conducting further studies inside
and outside of China to trace the origin of SARS-CoV-2 These studies were multifaceted and aimed at
detecting antibodies against SARS-CoV-2 in hundreds of thousands of human blood samples from June
2020 and onwards stored at the Wuhan Blood Service. These analyses would be conducted by both
local and international laboratories using state-of-the-art serological methods. It was also agreed to re-
do the review of approximately 76,000 medical files from individuals presenting with fever, severe
acute respiratory illness, pneumonia of unknown etiology or influenza-like-illness as the first review
outcome was hampered by the use of early case-definitions. Further recommendations targeted the
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animal origin and included detailed upstream analyses of animal trade and serological sampling of
humans and animals involved in farming and trading fur animals sold at the HSM, as well as the history
of animal and product trade in various markets across Wuhan. Additionally, human serosurveys and
surveys of susceptible animals on farms in China, South-East Asia and beyond were recommended to
identify viruses related to SARS-CoV-2, with a particular focus on targeted surveys of geographical
areas with fur farms.
In November 2021, the WHO Director-General established SAGO, pursuant to the World Health
Assembly Resolution 73.1 (WHO, 2020d), to develop a Global Framework on identifying the source
of emerging and re-emerging pathogens (including SARS-CoV-2) and the route of introduction to the
human population (WHO, 2024a). This framework has been applied to the SARS-CoV-2 investigations
and the outputs are outlined in this report.
Aim of SAGO’s independent assessment of the origins of SARS-CoV-2
As provided in its Terms of Reference, the SAGO was established by the WHO Director-
General to advise the WHO Secretariat on technical and scientific considerations regarding
emerging and re-emerging pathogens, and is composed of experts acting in a personal capacity.
SAGO was tasked by WHO to review all evidence (e.g., scientific peer-reviewed papers and
reviews, available unpublished information, field investigations, interviews, and other reports
including audit findings, and government reports) that evaluated early human COVID-19 cases,
animal infections, and any other indicators relevant to the origins of SARS-CoV-2 in order to
provide the WHO Secretariat with an independent assessment of what is known about the
origins of the COVID-19 pandemic and recommend further studies to be conducted.
Its mandate was to provide an independent assessment of the origins of SARS-CoV-2 and evaluate all
available evidence, including data from all field missions to China (WHO, 2021) and any data available
since the first identification of SARS-CoV-2, notably studies published or otherwise made available
since the publication of SAGO’s preliminary report in 2022 (SAGO, 2022), that may support or dispute
all reasonable hypotheses of the origins of the virus and its spillover into humans.
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According to SAGO’s Terms of Reference (WHO, 2021b), it was tasked to advise WHO on the
development of a Global Framework to define and guide studies and field investigations required to
investigate the origins of newly discovered, previously unknown pathogens with epidemic or pandemic
potential (“Disease X”). The Global Framework, published in 2024 serves as a comprehensive reference
for enhancing global programmatic and policy-related preparedness for ‘Disease X’ (WHO, 2024a,
Venter, 2023). It provides Member States with comprehensive guidance on the studies needed to
investigate the origins of emerging and re-emerging pathogens, offering a structured approach to
evaluating and controlling future emerging health threats before they spread, and applied here for the
investigation of the origins of SARS-CoV-2.
Methods
Since its establishment, SAGO (WHO, 2021a) has met 52 times – including 27 plenary sessions and 25
working group sessions — both in-person and virtually, to examine available evidence and review
published and pre-print scientific reports related to the origins of SARS-CoV-2.
To ensure all available evidence was obtained, a comprehensive and multidisciplinary approach was
used to assess a wide array of both published and unpublished studies, encompassing a diverse variety
of data sources. SAGO relied primarily on peer-reviewed scientific publications for the majority of its
deliberations. However, preprint materials, private research submissions, and governmental or
government intelligence reports were also reviewed to identify novel scientific findings and to
understand how these sources generated hypotheses related to SARS-CoV-2 origins. Where gaps in
data were evident, SAGO has articulated those limitations and continues to recommend additional
studies that may enhance our understanding of the pandemic’s emergence.
Two systematic peer-reviewed literature reviews were conducted in 2022 and 2023, with regular
updates in 2024 and 2025 to incorporate any new data. Original and review articles on SARS-CoV-2,
COVID-19 and other coronaviruses were assessed, including, but not limited to, the following topics:
surveillance in humans, animals and the environment; animal markets, early human cases, acute
respiratory infection surveillance, pneumonia, severe acute respiratory infections; animal susceptibility
to SARS-CoV-2, precursor virus strains; surveillance and research of bat coronaviruses in China and
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South East Asia, potential intermediate hosts, reverse zoonoses, molecular epidemiology, evolution,
serological surveys; laboratory biosafety, laboratory and farm biosecurity, field acquired infections,
laboratory acquired infections, virus gain of function research, origins. Published scientific papers and
pre-prints were reviewed and primarily was the focus of this review. However, while not treating the
same as peer-reviewed literature, SAGO considered carefully as any relevant media reports or other
data sources relevant to the origins of SARS-CoV-2. Data was sought from various databases where
sequences and meta-data from early cases, animals or metagenomic data were deposited, including
GenBank, GISAID and the Chinese National Genomics Data Center database (China National Center
for Bioinformation, 2022). The WHO secretariat wrote to authors of published and pre-published (pre-
print) literature to obtain further information about relevant studies, background data and/or reviews
and contacted databases requesting access to sequences from early cases.
The WHO Secretariat arranged presentations for SAGO members from scientists representing a range
of disciplines and institutions (see acknowledgements) including from the Chinese Center for Disease
Control and Prevention (China CDC); Beijing Institute of Genomics, Chinese Academy of Sciences;
National Health Commission of the People’s Republic of China; Institute of Pathogen Biology, Chinese
Academy of Medical Sciences; University of Arizona; University of California, San Diego; Technical
University of Denmark, and the University of Sydney, Australia.
In addition to reviewing publicly available peer reviewed information, SAGO also considered pre-
prints, interviewing authors of selected papers, unpublished data and findings provided through solicited
and unsolicited communications to the Secretariat (through emails, reports and presentations to SAGO),
as well as careful reviews and intelligence reports by governmental agencies, ensuring that all relevant
information potentially related to the origins of SARS-CoV-2 was evaluated. This included discussions
with journalists based in China during the start of COVID-19 who conducted interviews with people in
and surrounding Wuhan involved in animal raising and trading.
Throughout this process, SAGO applied the Global Framework for investigating novel pathogens
(WHO, 2024a) to ensure a systematic and transparent scientific review which underscores the
importance of a collaborative, evidence-based approach to understanding and mitigating global health
18
risks. The results section in this independent assessment is structured according to the six elements
outlined in the Global Framework (box 1).
Box 1. Elements of the WHO global framework to define and guide studies into the origins of emerging
and re-emerging pathogens with epidemic and pandemic potential (WHO, 2024a)
· Early investigations of the first identified cases/clusters/outbreaks to identify potential sources
of exposure, collection of samples at the source, define the characteristics of the novel pathogen
involved for establishment of diagnostic assays.
· Human studies to understand the epidemiology, including clinical presentation, modes of
transmission, pathology and earliest presence in syndromic surveillance samples.
· Human/animal interface studies to identify potential animal reservoirs, intermediate hosts and
reverse zoonoses.
· Environmental and ecological studies to identify insect vectors or other sources of infection as
well as earliest presence in the environment.
· Genomics and phylogenetics studies to identify precursor strains, genomic characteristics,
evolution in intermediate hosts and humans and spatial distribution over time.
· Biosafety/biosecurity studies to determine if a breach in laboratory or research activities may
have been associated with the first cases.
19
Results
Early investigations and human cases
Early studies reported varying dates for the earliest symptom onset. One publication cited the earliest
reported case had symptom onset on 8 December 2019 (Li et al., 2020a), whereas others identified cases
with symptom onset of 1 December 2019 (Huang et al., 2020; Allam, 2020). It was reported that the
case with symptom onset of 1 December 2019 was linked to the HSM, whereas the case from 8
December 2019 was not. Using the initial case definition for novel coronavirus-infected pneumonia
(NCIP) developed by China CDC, a suspected case was a patient meeting four criteria: a) pneumonia
with fever; b) lung radiographic evidence (e.g. ground glass opacity); c) abnormal white cell count; and
d) no improvement after three days of antibiotics. Alternatively, a case could meet the first three criteria
and have an epidemiological link to the HSM or contact with a patient with similar symptoms (Li et al.,
2020a). Li et al. (2020) reviewed 425 of the earliest laboratory-confirmed COVID-19 patients finding
that 55% of the 47 cases with onset of illness before 1 January 2020 were linked to the HSM compared
with only 8.2% of the subsequent cases reported between 1 - 22 January.
It was later recognised that SARS-CoV-2 infection may present with no symptoms or with mild illness,
and therefore it is likely that early cases may not have been detected by early surveillance efforts. Li et
al. (2020) concluded that the exclusion of cases not meeting the case definitions applied at the time,
along with cases featuring mild or no symptoms, contributed to an underestimation of the number of
cases, and that transmission could have occurred in the community, independent of the HSM, before 1
January 2020 (Li et al., 2020b; Wang et al., 2020). In support of the hypothesis that earlier cases with
mild symptoms may have been missed, there was a case with an onset of mild symptoms of cough and
fever on 1 December 2019, that was linked to the HSM. However, the case was later hospitalized on 26
December 2019 with palsy and related eye-movements suggesting CNS affection and interstitial
pulmonary changes by CT scan of the lungs, but it was concluded by the review panel to have suffered
from aspiration due to his CNS affection, possibly ignoring the early onset of cough and fever (2021c).
20
Early estimations of the basic reproduction number (R0) in Wuhan in December 2019 and early January
ranged from 2.24 to 3.77 (Zhao et al., 2020a; Zhao et al., 2020b; Lin et al., 2020).
In December 2020, Wuhan CDC reviewed the National Notifiable Disease Reporting System
identifying 174 cases of COVID-19 with symptom onset in 2019 in Wuhan (100 laboratory confirmed,
74 clinically diagnosed). The case definition was iteratively revised based on findings regarding the
transmissibility of SARS-CoV-2 (WHO, 2021). The members of the WHO-China Joint Mission in
February 2021 were informed that 32.8% of the 174 early cases (for which information was available)
were associated with the HSM in Wuhan, suggesting that the HSM played a significant role in the early
phases of the epidemic, while 22.6% of cases had association with another market. Some 44.6% of the
early cases had no history of market exposure, indicating unrecognized community transmission (WHO,
2021). This is consistent with a number of papers published in 2020, where 28-66% of early cases had
documented links to the HSM, suggesting transmission of other cases was occurring outside of the
market (WHO, 2021; Bosco-Lauth et al., 2021b; Xiao et al., 2021; Crits-Christoph et al., 2024).
Geospatial analyses of the earliest known 174 COVID-19 cases concluded that a disproportionate
number of affected individuals had worked at or visited the HSM, and/or that an unexpectedly large
proportion of 174 early cases were living close to the HSM (Worobey et al., 2022a). Although this
suggests opportunity for human exposure to SARS-CoV-2 at the market, spatial epidemiological data
and early human virus sequences from Wuhan infer the importance of the area in or around the market
(Wu et al., 2022), but do not provide evidence of transmission from animals at the market, nor determine
when nor where the virus first infected humans or began transmitting between humans. The same spatial
focus on the HSM is apparent when using all reported early human cases (beyond the earliest 174 from
December 2019), and also when those cases for which there was a known link to the market are
excluded. Potentially, there was ascertainment bias due to the availability of clinical and laboratory
data from certain sites closer to HSM, or this reflects treatment-seeking behaviour.
Using social media-derived case data, Worobey et al. also found the distribution of COVID-19 cases
was similar to that of the spatial distribution of the population by February 2020 (Worobey et al.,
2022a). Similar results were found by another group of researchers that analysed spatial distribution of
21
cases over January to February 2020 (Peng et al., 2020). This suggests the initial link to the market was
lost after some weeks of the outbreak, consistent with secondary spread in the population.
During the first joint international mission in February 2020 (WHO, 2020), the team reviewed
surveillance data related to the population of Wuhan, the epicentre of the outbreak at the time, and the
surrounding Hubei Province. Discussions and review of routine surveillance data from official disease
surveillance systems, including on severe acute respiratory illness, influenza-like illness (ILI), fever,
and pneumonia of unknown etiology systems from 2015-2019, did not reveal evidence of earlier
COVID-19 outbreaks in Wuhan or elsewhere in China. However, there were many questions
unanswered, including the reasons behind the increase in ILI in children and adults at the end of 2019
in Wuhan, which could be due to other circulating pathogens like influenza and RSV (WHO, 2020).
Furthermore, a review of official mortality data from Wuhan and Hubei Province provided to the WHO-
China mission team of 2021 from week 14-2019 to week 14-2020 did not identify significant peaks in
mortality prior to December 2019, contrary to the pneumonia-associated mortality that was evident in
early January 2020, followed by a rapid rise of all-cause and pneumonia-specific mortality during week
3 of January 2020.
Chinese scientists followed the WHO-China joint-report recommendation to examine blood samples
collected before 2020 in Wuhan, China and reported that no SARS-CoV-2-specific antibodies existed
among 43,850 samples from 32,484 blood donors (Chang et al. 2022), indicating that there was no
evidence of infection of SARS-CoV-2 before December 2019 within the study population area.
In summary, available evidence provided by China during the 2020 and 2021 missions did not identify
unusual clustering or deviation from trends in the weeks and months preceding these first reported cases
in early December 2019. However, it was noted then and remains relevant now that the stringent case
definition, which included ‘COVID-19 specific pulmonary changes’ (e.g. ground glass opacity) on CT
scans used for reviewing 76,253 medical files, limits the interpretation of these findings, with milder to
moderately severe cases inevitably being missed.
Based on phylogeny and empirical mutation frequencies, initial and updated analyses considering all
currently available sequence data, Pekar et al. proposed that a single introduction of SARS-CoV-2 into
22
the human population is “highly unlikely” (Pekar et al., 2022; Hensel and Débarre, 2025; Pekar et al.,
2025). These findings suggest two slightly different but distinct genetic virus variants: lineage A and
lineage B. Human infection with lineage B is estimated to have occurred around 18 November 2019
(range 23 October-8 December) and predates the initial infection of humans with lineage A by days to
weeks. In view of the inferred extinction rate of early lineages, approximately eight precursor lineages
(95% Bayesian confidence limits, 2 to 25 introductions) would be required to make the survival of two
founding lineages likely (Tang et al., 2021).
SAGO discussed and considered the importance of retrospective investigations on clinical samples bio-
banked in other areas of the world in 2019 to identify potential circulation of SARS-CoV-2 prior to the
official reports of cases in Wuhan, China. As noted in SAGO’s preliminary report published in June
2022, (SAGO, 2022) retrospective detection of early SARS-CoV-2 from clinical samples were
published from Italy (Lombardy) in October and November 2019 and France in December 2019 using
IgG serological assays, followed by serum neutralisation assays (Apolone et al., 2021; Carrat et al.,
2021). As a result of these initial findings, the WHO Secretariat arranged for further testing of the
remaining clinical samples and verification in independent laboratories. The results could not be
reconfirmed by an independent laboratory (Erasmus University Rotterdam, Netherlands) using IgG
ELISA and virus neutralization test (VNT) (WHO, 2021). Other reports of early SARS-CoV-2
detections in clinical samples that tested positive by RT-PCR on respiratory samples or ELISA, on
serum samples that could not be confirmed by VNT, were reported from Italy (September 2019-March
2020), France (November 2019-January 2020), Spain (unpublished) and the USA (no positive samples
could be confirmed before December 2019). Table 1 summarises published studies of pre-pandemic
samples tested for SARS-CoV-2. However, these have not been confirmed by other laboratories;
positive RT-PCRs should be confirmed by sequencing.
23
Table 1: Pre-pandemic samples tested (published studies)
Country Study period Sample Results Number of positive samples Number of Technology used to analyse References
of the type for (date of earliest detection) samples tested samples
samples samples
Italy September Blood Positive 111 of 959 showed 959 RBD-ELISA (Apolone et al., 2021)
2019 - March for SARS-CoV-2 antibodies microneutralization assay
2020 SARS-Co (September 2019).
V-2 6 of 111 positive through
antibodies microneutralization test (October 111
2019)
November Skin Positive 1 1 RNA fluorescence in situ (Gianotti et al., 2021)
2019 biopsy (November 2019) hybridization (FISH) (positive)
RT-PCR (negative);
November Plasma Positive 11 (November 2019) 290 (234 liver Antibody RDT + CLIA (Gragnani et al., 2021)
2019 - March diseases, 56 blood No neutralization assay
2020 donors)
September Throat Positive 1 39 RT-PCR (Amendola et al.,
2019– swab (December 2019) 2021)
February 2020
France November Serum Positive 13 9,144 ELISA microneutralization (Carrat et al., 2021)
2019 samples (4 November 2019) assay
-March 2020
December Respirator Positive 1 14 RT-PCR (Deslandes et al.,
2019 – y samples (December 2019) 2020)
January 2020
24
Country Study period Sample Results Number of positive samples Number of Technology used to analyse References
of the type for (date of earliest detection) samples tested samples
samples samples
USA Oct 2019 Nasophary Positive 7 2,321 RT-PCR (Hilt et al., 2022)
- March 2020 ngeal (mid-January 2020)
swabs
January 2020 - Blood Positive 9 24,079 ELISA (Althoff et al., 2021)
March 2020 (January 2020)
December Blood Positive 106 (reactive) of 7389 samples 7,389 total blood ELISA microneutralization (Basavaraju et al.,
2019 -January (mid-December 2019). donations assay 2021)
2020 84 of 90 had neutralizing activity collected
(mid-December 2019).
90 further tested
(ELISA/micro-
neutralization
2011-2020 Serum Positive 3 – (2020 samples) 239 Surrogate virus neutralization (Chandler et al., 2021)
samples 1 – (2019 sample - at limit of assay
from wild detection, not confirmed by
deer another virus neutralization test)
0 (from 2011 – 2018)
Norway December Serum Positive 36 6,520 eCLIA + CLIA (Eskild et al., 2022)
2019 - samples (1 from December 2019) No neutralization assay
December from
2020 pregnant
women
25
Testing for SARS-CoV-2 in animals and the environment at the Huanan
Seafood Market
The 2021 WHO-China report and multiple studies have suggested that the HSM played an important
role in SARS-CoV-2 transmission, either through the sale of animals known to be susceptible to
SARS-CoV-2 infection, amplification of human transmission (spillover having occurred elsewhere), or
as a possible site of spillover via contact with infected animals sold at the market (WHO, 2021c; Liu
et al., 2023; Xiao et al., 2021; Pekar et al., 2022; Worobey et al., 2022a; Crits-Christoph et al., 2024).
The HSM was supplied with farmed wildlife from farms located in the prefectures of Tianmen, Xiaogan,
Jingmen, Suizhou, Xiangyang, and Huangshi, also at the county level in Jianli, Wuxue and Jingshan -
within Hubei Province. Outside Hubei province, source farms were in the provinces of Heilongjiang,
Jilin, Shanxi, Henan, Hunan, Jiangxi, Guangdong, Guangxi and Yunnan (WHO, 2021). SAGO’s ability
to fully understand the significance of the HSM in the origins of SARS-CoV-2 is limited by the fact
that no precise information, including on the quantity, species and source locations, of the animals sold
at the HSM or other markets in Wuhan has been made available to WHO or SAGO to date or published.
It is important to note that the wildlife trade in wet markets is prohibited under Chinese law. As a result,
tracing the specific origins of animals sold at the HSM presents logistical and regulatory challenges.
These circumstances may also complicate the systematic documentation and sharing of related
information with WHO and international partners. It is also important to note that Xiao et al reported
on animals that were sold at the HSM from May 2017 and November 2019, including 38 live animal
species, including racoon dogs (Nyctereutes procyonoides), red foxes (Vulpes vulpes), mink (Neovison
vison) and masked palm civets (Paguma larvata), all of which are known to be susceptible to
SARS-CoV-2 infection (Xiao et al., 2021).
According to information provided to the international team in 2021, it is understood that on 30
December 2019, local Chinese public health authorities entered the HSM market and collected the first
environmental samples from the market stalls and environments, and that on 31 December 2019, a joint
team consisting of experts from four levels of China CDC conducted the investigation of HSM and
initiated epidemiological studies around the market. On midnight 1 January 2020, Chinese authorities,
26
following standard public health biosafety procedures in response to the outbreak of COVID-19, closed
the market for disinfection.
Between 1 January and 30 March 2020, Chinese authorities reportedly conducted interviews with
market sellers, collected samples from 457 animals in and around the market (including live rats, mice,
stray weasels, cats, and dogs, as well as from the carcasses of sheep, wild boars, bamboo rats, badgers,
muntjacs, hedgehogs and rabbits) and 923 environmental samples (e.g., from equipment, stalls and
drains) (Liu et al., 2023). Published reports and presentations to SAGO stated that all samples from
animals collected at the market tested negative for SARS-CoV-2. However, 73 environmental samples
collected from various locations and from surfaces inside the market were RT-PCR positive (Xiao et
al., 2021, Worobey et al., 2022a; Liu et al., 2023; Bosco-Lauth et al., 2021a; Crits-Christoph et al.,
2023; Wu, 2023). Further analysis by Crits-Christoph et al. (2024), using data shared by Liu et al.
(2023), performed spatial risk mapping based on SARS-CoV-2 RT-PCR and metagenomic sequence
detections in swabs from animal cages and other surfaces, as well as samples from sewage drains,
pinpointing specific market stalls (Liu et al., 2023; Crits-Christoph et al., 2024). The authors refined
the taxonomic comparison of animal genetic material by partially re-assembling sequence-read contigs.
At the HSM stalls, mitochondrial DNA hits from several susceptible species to SARS-CoV-2 were
detected, including from raccoon dog, hoary bamboo rat, and palm civet, with genetic traces of the
former two species particularly abundant across the wildlife market area, and some of these samples
containing high amounts of SARS-CoV-2 sequencing reads. Based on mitochondrial gene SNP typing,
geographic origins of the detected raccoon dogs were mapped to central or southern China. Liu et al.
(2023) confirmed presence of bat and pangolin DNA, but subsequent comparisons of detected nucleic
acids with the Barcode of Life Data System COX1 gene database by international scientists failed to
confirm the presence of bat or pangolin nucleic acids in market samples (Liu et al., 2023; Crits-
Christoph et al., 2024). These findings suggest that some animals, particularly raccoon dogs, known to
act as Sarbecovirus intermediary hosts, were present at the market before its closure on 1 January 2020,
though it cannot be concluded that the virus was introduced via these animals (Liu 2023b).
27
The report by Liu et al. (2023) confirmed the presence of two SARS-CoV-2 lineages; A and B, in
environmental samples from the HSM, and with a higher frequency of lineage B over A, consistent with
lineage B´s earlier inferred emergence (Liu et al., 2023).
Detection of SARS-CoV-2 in wild animals in China and South-East Asia
According to the 2021 WHO-China joint report, 2328 samples from wildlife were collected in
December 2019 — using non-structured, convenience sampling — all tested negative for SARS-CoV-2.
Additionally, 2995 samples from Hubei province (February-March 2020), and 27,000 samples for PCR
and 1914 sera were taken from other parts of China also yielded negative for SARS-CoV-2 (Annex C6
Reports Annexes) (WHO, 2021c).
The WHO Secretariat invited a number of scientists from China, including from the Centre for Infection
and Immunity Studies, School of Medicine, Sun Yat-Sen University, Guangzhou, China; Chinese
National Influenza Center (CNIC), National Institute for Viral Disease Control and Prevention, Chinese
Center for Disease Control and Prevention (CDC), China, to present research associated with testing
animal samples from Chinese provinces. In these presentations, the invited scientists reported that all
testing undertaken in animals in China did not detect the presence of SARS-CoV-2 virus (nucleic acid)
or antibodies.
The most detailed of these surveys was presented to SAGO in January 2022 by the Beijing Institute of
Genomics, Chinese Academy of Sciences, and Clinical Laboratory Center, National Health
Commission (NHC), who reported that by 30 November 2021, 32,479 animal samples had been
collected from 18 provinces including Hebei, Inner Mongolia, Liaoning, Jilin, Heilongjiang, Shanghai,
Jiangsu, Henan, Hubei, Hunan, Sichuan, Guizhou, autonomous region of Tibet, Gansu, Shaanxi,
Jiangxi, Ningxia and Qinghai. The scientists reported that no SARS-CoV-2-related nucleic acid were
found in 218 species from 13 orders including Rodentia, Carnivora, Artiodactyla, primates,
Lagomorpha, Pholidota and Erinaceidae. Furthermore, 1311 serum samples from livestock and poultry
(in Hubei and seven other provinces), and 2837 serum samples from dogs, cats, mink, foxes, and
raccoon dogs (collected in Henan, Shandong, Hebei and Hubei in autumn 2020 - precise dates were not
included in the presentation) all tested negative for SARS-CoV-2 antibodies. However, further details
28
about sample sizes, sampling schemes, specific animal species and numbers of animals tested,
methodology of laboratory testing, locations of farms, markets, and sources of animals were not
provided during this presentation (unpublished information presented to SAGO by Chinese Scientists).
Scientists in the Mekong Delta and South-East Asia (China, Thailand, Myanmar, Cambodia, Lao
People’s Democratic Republic, and Viet Nam) presented regional coronavirus research in various bat
species at a WHO regional technical surveillance workshop held in Bangkok, Thailand (October 2022).
Findings from the surveillance activities in Thailand (which is home to one third of all members of the
Rhinolophidae family) included partial sequences of new species of SARS-CoV-like coronaviruses
found in Rhinolophus bats. Researchers from Cambodia presented serological investigations which
indicated seropositivity to coronaviruses, filoviruses, and henipaviruses across diverse bat populations
and specifically in pteropid bats. Some gaps highlighted from these countries were the regional lack of
technology and capacity in labs to detect and characterize novel viruses, including a lack of funding to
conduct whole genome sequencing of the viruses, as well as biosafety capacities and training. These
limitations hamper the ability for researchers to characterise novel SARS-CoV related viruses identified
in bats and mammals in the region.
While the intermediate host(s) for SARS-CoV-2 has (have) not yet been determined, it is widely
accepted that precursor viruses for coronaviruses originate in bats (Zhou et al., 2021). Sixteen bat
species have been identified as potential sarbecoviruses carriers (Wu et al., 2022). Shortly after the
reports of the first cases of SARS-CoV-2, phylogenetic analyses identified the closest related precursor
strains to SARS-CoV-2, in bats detected from China (RaTG13; 2013; 96.1% identity) and later in Lao
People’s Democratic Republic (BANAL-52; 2020; 96.8% identity) (as seen in Table 2) (WHO, 2024a;
Temmam et al., 2022; Zhou et al., 2020b). Wu et al. (2022) tested 4270 bats pertaining to different
Rhinolophus species across China that yielded 146 novel Sarbecovirus genomes. None of the genomes
were closely related to SARS-CoV-2 (680 members of the highly relevant species, R. affinis were
included in the sample). Zhou et al. (2021) tested 283 bats from at least five Rhinolophus species and
also Hipposideros larvatus identifying novel Sarbecoviruses but none closely related to SARS-CoV-2
(Zhou et al., 2021). These are discussed further in the genomics section of this assessment.
29
Variability of virus prevalence and species distribution makes it difficult to define virus endemicity.
For instance, Wu et al. 2022 noted that the closest relatives to SARS-CoV-2 ‒ BANAL-52, BANAL-
103 and RaTG13 ‒ stem from Rhinolophus malayanus, R. pusillus, and R. affinis, respectively (Table
2 summarises the closest known coronavirus relatives to SARS-CoV-2, including their host species,
genome similarity, and geographic origin) (Wu et al., 2022).While some of these species may live
predominantly outside China, they also exist within China, but few samples have been tested to date.
Moreover, since the direct precursors to SARS-CoV-2 may have passed through an intermediate host,
bat distribution alone may not indicate the site of spillover. A recent paper (Havens et al., 2025)
analysed the hypothesis that zoonotic viruses require adaptation prior to zoonosis to sustain human-to-
human transmission. Based on Ebola, Marburg, influenza A, SARS-CoV-1 and SARS-CoV-2, there
was no change of selection immediately prior to a host switch. This implies that closely related precursor
viruses from bats might have transmitted directly to humans and subsequent evolution occurred in
humans. Nevertheless, the currently known precursor viruses are still too distant from SARS-CoV-2 to
have been the source of the early cases in Wuhan as discussed under the genomics section.
The search for viral precursors in potential intermediary hosts suffers from similar challenges, based on
limited sample size and geographic coverage in currently published studies. For example, He et al.
(2022) tested 1941 individual game animals (samples collected after February 2020) typically sold in
Chinese markets, including from the orders Rodentia, Carnivora, Lagomorpha, Eulipotyphla, and
Pholidota (pangolins), but none were reported as positive for Sarbecovirus (He et al., 2022). However,
in these analyses, only 95 raccoon dogs and 425 masked palm civets were tested ‒ both known
susceptible species. Additionally, animals in this study were mostly from natural habitats and not
targeting the animal production sites that had been recommended for testing in the 2022 SAGO report
(SAGO, 2022). Despite raccoon dog fur farming being legal in China, the sale of raccoon dogs in live
animal markets was halted (precise dates were not included in the presentation in which this information
was shared), and almost all samples that have been tested were collected after February 2020 (Xiao et
al., 2021). No results of surveillance studies on upstream wildlife value chains and wildlife farms have
been published or made available to SAGO, following the publication of the WHO-China 2021 report
despite requests (WHO, 2021c).
30
Table 2: Coronaviruses identified with highest similarity to SARS-CoV-2
Genome Originating Year
Animal Virus region, identified References
Species strain Identity to
SARS-CoV-2 country
Bat (Temmam et al.,
R. malayanus BANAL- 96.80% Laos 2020 2022)
52
Bat RaTG13 96.10% Yunnan province, 2013 (Zhou et al.,
R. affinis China 2020a)
Bat BANAL- 95.20% Laos 2020 (Temmam et al.,
R. pusillus 103 2022)
Bat Laos (Temmam et al.,
R. marshalli BANAL- 95.20% 2020 2022)
236
Bat Yunnan province, (Zhou et al., 2021)
R. pusillus RpYN06 94.48% China 2019
Bat Yunnan province, (Zhou et al.,
R. malayanus RmYN02 93.30% China 2019 2020a)
Bat Laos (Temmam et al.,
R. malayanus BANAL- 92.90% 2020 2022)
116
Bat Laos (Temmam et al.,
R. malayanus BANAL- 92.20% 2020 2022)
247
Bat RshSTT18 92.90% Cambodia 2010 (Delaune et al.,
R. shameli 2 2021)
Bat RshSTT20 92.90% Cambodia 2010
R. shameli 0
Malayan Unknown (seized (Xiao et al.,
pangolin PCoV- 92.40% during anti- 2019 2020)
Manis GDC smuggling (Liu et al., 2020)
javanica operation in (Zhou et al.,
China) 2020a)
Bat (Wacharapluesa
RacCS203 91.15% Thailand 2020
R. acuminatus dee et al., 2021)
Bat Yunnan province,
R. pusillus PrC31 90.70% 2018 (Li, 2021)
China
Malayan Unknown (Liu et al., 2020)
pangolin M. PCoV- 90.32% (seized during 2019
javanica 2020 anti-smuggling
operation in
China)
Malayan Unknown
pangolin M. MP789 90.20% (seized during 2019 (Liu et al., 2019)
javanica anti-smuggling
operation in
China)
31
After the SARS epidemic in 2002-2003, Chinese authorities discovered a second animal-to-human
spillover of SARS-CoV (referred to as SARS-CoV-1 in the remainder of this report) at the end of 2003
(Wang et al., 2005; Ye et al., 2020), and they ordered the destruction of civet cats and raccoon dogs in
the Xinyuan market in Guangdong province. During this process, culled animals were swabbed and
tested for SARS-CoV-1, identifying 14 of 18 as positive at the Xinyuan market, as well as identifying
antibodies to SARS-CoV-1 in masked palm civets in one of the four supplier farms in Guangdong
province.
From January to September 2004, breeding facilities for masked palm civets in 12 Chinese provinces
supplying animals to the Xinyuan market were systematically visited and the animals tested – results
from 1107 samples tested negative (Kan et al., 2005). Detected viruses were sufficiently characterized
to enable the retrospective reconstruction of genomic changes that occurred during the emergence of
SARS in 2002 in humans. As of June 2025, no additional data outside of the information provided in
the 2021 WHO-China report (WHO, 2021c) (refer to pages 99-106) has been made available to SAGO
or WHO on SARS-CoV-2 testing conducted on raccoon dogs and other susceptible species that were
commercially bred and had trade links to the HSM, or any markets in Wuhan city, Hubei Province or
within China, prior to December 2019.
Also, data has also not been made available from SAGO-recommended studies (SAGO 2022),
including the systematic random sampling of animal farms, hunters, animal traders, markets or market
sellers to and from the HSM. There is a need for more information, particularly from source farms
trading animals to wet markets, in order to determine the existence of early circulation and spillover
(WHO, 2022).
Animal infection experiments and reverse zoonoses
Reverse zoonosis of SARS-CoV-2 from humans to animals has been documented in wild, farmed, zoo,
and domestic animal species. As of October 2023, the World Organisation for Animal Health (WOAH)
reported 775 outbreaks in animals, across 29 species in 36 countries (World Organisation for Animal
Health, 2023). Susceptible species to SARS-CoV-2 infection belong to the families: Bovidae, Canidae,
Cebidae, Cercopithecidae, Cervidae, Cricetidae, Felidae, Hominidae, Hyaenidae, Mustelidae,
32
Procionidae, Viverridae, Hippopotamidae, Myrmecophagidae, Atelidae, Rhinocerotidae, Suidae,
Agamidae, Phasianidae, Anatidea, Castoridae, Muridae, Chlamyphoridae, Leporidae, Vespertilionidae,
Sciuridae, Didelphids and Procyonidae, with spillover potential from one animal species to another.
(Food and Agriculture Organization of the United Nations, 2023) (Annex 1 Table 1). In addition,
laboratory experiments have been conducted on animals to identify potential susceptible species that
could be considered in search of the SARS-CoV-2 reservoir and/or have the potential to create new
SARS-CoV-2 variants (Food and Agriculture Organization of the United Nations, 2023) (Annex 1
Table 2).
Although most SARS-CoV-2 zoonotic transmission documented has been from humans to animals,
some transmission has included spread among animals, and spillback to humans (Zhou and Shi, 2021;
Yen et al., 2022). Farmed mink exhibit both symptomatic and asymptomatic SARS-CoV-2 infections
and have been affected by large outbreaks before mass culling in several European countries in 2020
(Pomorska-Mól et al., 2021). In Denmark, culling of mink was recommended following the discovery
of the “cluster 5” SARS-CoV-2 variant, which infected 12 people during November 2020 (EFSA Panel
on Animal Health and Welfare et al., 2023). Outbreaks on mink farms in Poland were linked to a two-
year-old human strain of the B.1.1.307 lineage that carried mutations typical of mink adaptation,
suggesting undetected circulation in a previously unknown animal reservoir (Domańska-Blicharz et al.,
2023). SARS-CoV-2 transmission from hamsters to humans was also documented in China, Hong Kong
Special Administrative Region (SAR) when infected animals transmitted the virus to a pet shop owner,
as well as probable cat to veterinarian transmission in Thailand (Yen et al., 2022 ; Chandler et al., 2021;
Kuchipudi et al., 2022 ; Marques et al., 2022 ; Hale et al., 2022; Palermo et al., 2022 ; Caserta et al.,
2023).
Another example is white-tailed deer (Odocoileus virginianus), where SARS-CoV-2 has spread widely.
The Animal and Plant Health Inspection Service (APHIS) reported virus in 12.2% and antibodies in
31.6% of white-tailed deer in the USA (APHIS, 2023) – which thus could act as a reservoir for nearly
extinct SARS-CoV-2 variants. (Chandler et al., 2021; Kuchipudi et al., 2022 ; Marques et al., 2022;
Hale et al., 2022; Palermo et al., 2022; Caserta et al., 2023).
33
Environmental investigations
The presence of SARS-CoV-2 RNA was reported in wastewater/sewage samples taken in Milan and
Turin, Italy, in December 2019 (La Rosa et al., 2021). Positive signals for SARS-CoV-2 were obtained
by nested RT-PCR and further confirmed by sequencing of the amplicon, but results could not be
verified by an independent laboratory at the Erasmus Medical Centre, Netherlands, a collaboration
which was facilitated by WHO. Further next-generation sequencing (NGS) and metagenomic studies
on those positive samples may yield more sequencing data, as near-complete genome sequences may
determine if there was any genetic variation from the SARS-CoV-2 strains circulating in China during
that period – noting that it is challenging to obtain full genomes from wastewater.
Following the publication of the SAGO preliminary report in 2022, a further study of wastewater
samples obtained from Brazil in November and December 2019 provided sequences covering about
25% of the SARS-CoV-2 genome using NGS (Fongaro et al., 2021). The results from these samples
should also be confirmed by an independent laboratory. Additional sequencing data may be useful to
determine the phylogenetic relationship to the Wuhan strain. Wastewater samples from various
additional countries at the time did not yield positive results (WHO, 2022).
Related to the ‘cold chain’ hypothesis, one more recent paper by Li et al published since the SAGO
preliminary report results of a large surveillance study of the cold chain from July 2020 to July 2021,
finding 1455 positive in more than 55 million samples taken across China (positivity of 0.26 per 10,000)
(Li, 2022). This demonstrated a low risk of contamination of frozen products even with high incidence
(and virus shedding) in humans, it should be noted that this surveillance did not cover the late 2019
period.
Genomic Investigations
As stated above, SARS-CoV-2 belongs to the Betacoronavirus pandemicum species in the Sarbecovirus
subgenus of Betacoronavirus. The genome organization of SARS-CoV-2 includes a cap structure at the
5’ end, a poly-A tail at the 3’ end, and 13-15 open reading frames in different variants, flanked by 5’.
34
and 3’ untranslated regions critical for viral RNA synthesis (Kim et al., 2020; Parker et al., 2021). The
S protein is essential for receptor binding and viral entry. Two features distinguish the SARS-CoV-2
genome from SARS-CoV-1 and SARS-CoV-like bat viruses: 1) mutations in the receptor binding
domain (RBD) that appear to optimize its binding to the human ACE2 receptor (as well as that of other
susceptible species), and 2) insertion of 12 nucleotides in the spike protein that result in a functional
polybasic furin cleavage site (FCS) RRAR at the S1–S2 boundary of the spike protein and predicted
acquisition of three O-linked glycans around the site (Andersen et al., 2020). This may create a ‘mucin-
like domain’ that shields epitopes and enhances immune evasion.
One of the viruses currently known to be closest to SARS-CoV-2 (RaTG13) was described along with
an original characterization of SARS-CoV-2 by Zhou et al. (Zhou et al., 2020b) An addendum to this
paper mentions that the virus material had been available since 2012/2013 at the Wuhan Institute of
Virology in the form of an uncultured original animal stored sample (ID4991) with published partial
sequence characterization in 2016, amended to near full sequence characterization in 2018, renamed
RaTG13 and published on GISAID (accession number EPI_ISL_402131) on 24 January 2020 (Zhou et
al., 2020b; Ge et al., 2016).
After the first identification and sequencing of SARS-CoV-2, comparison of the partial sequence led
researchers to complete sequencing of the full genome of RaTG13. However, the RaTG13 genome has
a low similarity with SARS-CoV-2 in the critical RBD of the spike protein (only 11 of 17 receptor
contact residues are conserved). Three progenitor bat viruses described from Northern Lao People’s
Democratic Republic in 2022 have both the ability to enter human cells via the ACE2 receptor and a
very high similarity in the RBD with SARS-CoV-2 (Temmam et al., 2022). BANAL-52 and BANAL-
103 show only one amino acid difference against SARS-CoV-2 in the RBD. BANAL-52 also has high
homology on full genome level (96.8%; compared to RaTG13 at 96.1%). However, these viruses are
too distant to be considered direct progeny of a common ancestor with SARS-CoV-2 but rather
represent mixed populations of viruses stemming from recombination and mutation events in a common
ancestor (Xiao and Whitney, 2021; Patiño-Galindo et al., 2021).
35
Sarbecoviruses have mosaic genomes that result from multiple recombination events in virus
populations existing mainly in Rhinolophus bats, while individual viruses may spill over into other
animals, where they are in isolation from the original reservoir population. SARS-related viruses
discovered in pangolins may be one example of many (Lam et al., 2020; Xiao et al., 2020). Genetic
recombination causes genomes to be similar in certain parts, while other parts are less similar and appear
less closely related. Genome recombination makes the tracing of genetic lineages difficult, as the
number of differences between two given genomes no longer reflects the same time distance from
common ancestors given the disruption recombination poses for molecular clock analysis.
Recombination is also a possible source of novel gene elements such as the FCS present in
SARS-CoV-2, which is not found in any of the known closely related genomes (Zhou et al., 2021).
Furin cleavage site elements - similar but not identical to those in SARS-CoV-2 - are commonly found
in S proteins of members of the subgenera Embecovirus, Hibecovirus and Merbecovirus such as HKU1,
OC43, and MERS-CoV that typically contain 2-3 arginine and optionally an additional lysine moiety
(Andersen et al., 2020; Stout et al., 2021). A polybasic FCS with an additional arginine moiety has also
evolved upon repeated serial passaging in mice in MERS-CoV, termed MERS-CoV MA-30 (Li et al.,
2017; Lisewski, 2024). The FCS in this virus (PRRVR) resembles that in SARS-CoV-2 (PRRAR), but
the nucleotide coding of identical amino acids is different between these viruses. PRRVR-containing
viruses have occurred sporadically during the SARS-CoV-2 pandemic in humans, but these were never
fixed in the population and have no evolutionary link to early SARS-CoV-2 strains or hypothetical
precursors, making them less relevant for understanding the origin of the FCS in SARS-CoV-2. In 2025,
a merbecovirus HKU5-CoV lineage 2 virus was identified in Pipistrellus bats in China that can use
human ACE2 as a cell entry receptor and exhibits a broad host tropism. Extensive and additional studies
of HKU5-related, ACE2 engaging viruses revealed a distinct interaction site and receptor binding
domains that make any cross-immunity following SARS-CoV-2 contact unlikely. Several
merbecoviruses possess FCS with two or three basic residues (Park et al., 2025). The ability of HKU5-
CoV lineage to infect human ACE2-expressing cell lines and human respiratory and enteric organoids
underscores its zoonotic potential (Chen et al., 2025). Several studies by Damas (2020), Conceicao
(2020), and Briggs (2023) have found that SARS-CoV-2 exhibits a broad ACE2 receptor-binding
36
spectra using SARS-CoV-2 isolates or pseudo-virions, including in various bat species (e.g. little brown
bat, Egyptian fruit bat), domestic and wild animals (e.g. pangolin, fox, civet, camel, ferret, rat and
squirrel); Bovidae and Cricetidae; and marine animals (e.g. sea lion, minke whale) (Damas et al., 2020;
Conceicao et al., 2020; Briggs et al., 2023). Affinity binding assays formerly suggested that pig ACE2
receptors were highly susceptible to transduction by SARS-CoV-2 S pseudo-virions, but recent reports
suggest pigs have low levels of ACE2 expression in their respiratory tract and therefore may not be
susceptible to infection (Carossino et al., 2024). This evidence expands on the list of animals that are
capable of being potential intermediate hosts of the virus. However, further substantial evidence is
required, including virus detection and isolation from these species to confirm their role/importance as
intermediate hosts.
Since the start of the pandemic, SARS-CoV-2 continues to evolve, resulting in the emergence of a
significant number of variants of interest and of concern (WHO, 2020e). With millions of SARS-CoV-2
genome sequences published in publicly available databases (over 15 million in GISAID as of 30 April
2025), thousands of single nucleotide variants (SNVs) have been identified. Variants that differed
significantly from previous variants gave rise to new waves of infection (WHO, 2020e).
The emergence of SARS-CoV-2 variants of concern (WHO, 2020e) through mechanisms such as
reverse zoonoses or spillover of novel coronaviruses from animals to humans requires continued
surveillance and investigation of any novel SARS-CoV-2 or other SARS-CoV-like variants that may
give rise to renewed waves or to new epidemics or pandemics (WHO, 2020; Chatterjee et al., 2023).
WHO has made requests to the Chinese government from the onset of the pandemic to release publicly
and/or provide WHO and SAGO with available sequences related to early SARS-CoV-2 infections.
While the initial SARS-CoV-2 genome was released quickly and allowed for the development of
diagnostic assays, other essential sequences only became available much later, with additional
SARS-CoV-2 metagenomics data from samples collected at the HSM in January 2020 only released by
China CDC in 2023 when an earlier preprint around investigations at the HSM was being prepared for
final publication in Nature (Liu et al., 2023). SAGO was made aware of this additional evidence only
upon its release by international researchers who analysed host DNA data from HSM previously
37
generated but not previously released by Chinese researchers. SAGO released a statement on the
importance of sharing genomic data rapidly and for international researchers to engage with the owners
of the data to ensure optimum analysis and timely release of data after emergence of novel pathogens
(WHO, 2023c). The WHO Secretariat contacted the China National Center for Bioinformation
requesting access to 508 SARS-CoV-2 sequences from patients in January-February 2020 uploaded to
the National Genomics Data Center by authors investigating early cases (China National Center for
Bioinformation, 2022). To date this sequence data has not been released.
Biosafety & Biosecurity Investigations
Laboratory-acquired infections and accidental pathogen release due to breaches in laboratory biosafety
and biosecurity have occurred in isolated but well-documented events throughout history and remain a
concern worldwide (Blacksell et al., 2024; Ristanović et al., 2020; Pedrosa and Cardoso, 2011;
Weinstein and Singh, 2009; El Jaouhari et al., 2022; Wurtz et al., 2016). Strict biosafety standards
published by international and national bodies work to minimise the risk of such events (WHO, 2020a;
Government of Canada, 2025; Centers for Disease Control and Prevention, National Institutes of
Health, 2020). WHO has published guidance to support laboratories and research institutions in
implementing these standards effectively, such as the WHO Laboratory Biosafety Manual (4th edition),
which provides comprehensive frameworks for risk assessment and mitigation in handling infectious
agents (WHO, 2020a).
Additionally, national biosafety guidance for laboratories has been published by authorities in several
countries including Australia and New Zealand, Canada, and the USA, as well as the European union
which provide detailed protocols for containment, equipment usage, and personnel training, ensuring
safety and compliance with international norms.
To date, no official information or documentation has been provided to WHO or SAGO to analyse the
biosafety and biosecurity practices and procedures in laboratories in Wuhan, including the WIV and the
Wuhan Centers for Disease Control. Representatives of the WIV laboratory provided verbal assurances
that appropriate procedures were and are being followed correctly, although no physical inspections
38
were done by the WHO-China international team in 2021 (WHO, 2021). No access has been approved
or provided to enable the independent verification or investigation of biosafety and biosecurity
measures in either laboratory, such as occupational health records, results of previous audits (including
biosafety reviews or biosafety evaluations), and any documentation of potential biosafety and
biosecurity breaches occurring in the months or years leading up to the first reported cases, as
recommended in the SAGO preliminary report (SAGO, 2022). In the biosafety statement published for
the recently identified bat merbecovirus, BtHKU5-CoV-2-023, that can utilize human ACE2 receptors
for cell entry, the authors state that “the experiments related to virus isolation and cell assays of
BtHKU5-CoV-2-023 were performed in a BSL-2 plus negative pressure laboratory following standard
operating procedures with necessary personal protection and approved by the WIV Institutional
Biosafety Committee according to a bio-risk assessment procedure (including the viral genome
sequence and its phylogenetic relationship to known human viruses, human receptor utilization, cell
tropism, prevalence in domestic animals and humans, and pathogenicity and transmission in animal
models) (Chen et al., 2025). Whereas SARS-CoV-2 has now been reclassified as risk group -2 in view
of its endemic status with widespread distribution and population immunity, countries should consider
classification of animal-derived coronaviruses with known or likely zoonotic potential, including bat-
derived CoV, as higher risk group pathogens. SAGO recommends that biosafety and biosecurity
measures for work involving potential zoonotic bat coronaviruses should be guided by a comprehensive
risk assessment, following the WHO Laboratory Biosafety Manual (4th edition) (2020) and the WHO
Laboratory Biosecurity Guidance (2nd edition) (WHO, 2024a).
A number of reports have also been published by government agencies (see later section for review of
these reports), which have evaluated the possibility of a laboratory leak at the start of the COVID-19
pandemic. WHO has requested access to the source materials and data used by government agencies in
the development of these reports, but these requests have not been granted. WHO received a response
from the German government the preparation of the report was ongoing and would revert once this
process is finished.
39
SAGO continues to recommend the investigation of all reasonable hypotheses for the origin of
SARS-CoV-2 as outlined in their preliminary report2 (SAGO, 2022).
SAGO continues to recommend: on-site laboratory assessments through interviews with laboratory staff
and officials from facilities in and around Wuhan; a review of all laboratory work and materials
documentation and digital inventories, biosafety and biosecurity records; risk assessments for activities
with pathogens (risk group 2 or higher) and review of risk control strategies; and a review of all
laboratory staff absenteeism reports and/or health complaints during 2019 (SAGO, 2022). In line with
this recommendation, WHO Secretariat wrote to the Government of China to request further
investigations, audits and other relevant documentation and interviews with staff at the WIV and Wuhan
CDC laboratory. However, this has been refused, no audit files have been made available for review
and, to date, no scientific data or evidence has been made available to SAGO or WHO to evaluate
whether a laboratory incident could have initiated the COVID-19 pandemic. The Government of China
has instead proposed that similar investigations be conducted in laboratories in other countries where
coronavirus research or reverse genetics studies have been carried out (State Council Information
Office, 2025).
Since information needed to assess the hypothesis of a lab related event, either during field
investigations or a breach in laboratory biosafety - has not been made available to WHO or SAGO, it
was not possible for SAGO to evaluate this hypothesis. Therefore, this possibility cannot be confirmed
nor eliminated. SAGO remains open to any new information that may further the evaluation of any
reasonable hypothesis grounded in science.
2
It is noted that one author of this report (Dr Maria Guzman) does not agree with the inclusion of evaluating the
possibility of introduction of SARS-CoV-2 to the human population through a laboratory incident.
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SAGO’s Evaluation of other reports on the hypotheses of the origins of
SARS-CoV-2 spillover into the human population
SAGO relied primarily on peer-reviewed scientific publications for the majority of its deliberations.
However, SAGO also reviewed available reports and government-produced intelligence reports to
understand how these sources generated hypotheses related to SARS-CoV-2 origins.
To date, there have been several groups (both scientific and non-scientific) and governmental agencies
convened to evaluate the origins of SARS-CoV-2. SAGO has reviewed and considered published peer
reviewed scientific reports from the most relevant groups and governmental or intelligence agencies
with the aim to seek out novel scientific evidence or intelligence that may help guide the discovery of
SARS-CoV-2 emergence into the human population. SAGO regarded scientific investigations that were
grounded in science and peer reviewed as the basis of our deliberations. More comprehensive
summaries of the most notable scientific reports were reviewed and are provided in Table 3A.
Secondary to this, SAGO evaluated governmental or intelligence reports to identify any novel scientific
evidence and to understand how their hypothesis was generated, however we recognise potential
political bias that may have driven some of these reports. More details are summarised in Table 3B.
Finally, SAGO evaluated a few reports, by civil movements, some that were co-authored by scientist,
that were sent directly to SAGO and publicised in the media, to provide a scientific perspective by
SAGO experts.
Published Scientific Reports (Summarised in Table 3.A)
In October 2022, several members of the Lancet COVID-19 Commission presented a brief analysis to
SAGO of their findings of the origins of SARS-CoV-2 (Sachs et al., 2022), as well as a separate analysis
by Keusch et al. (Keusch et al., 2022). While no new evidence was presented to SAGO that could
support either hypothesis, the Lancet report focused on the genomic structure of the virus (specifically
the furin cleavage site), and encouraged that WHO and governments should intensify the search for the
origins of SARS-CoV-2 and investigate both the possibilities of a zoonotic origin and research-
associated origin (Sachs et al., 2022). The zoonotic spillover hypothesis was presented in detail with
options of natural spillover from a bat reservoir, via an intermediate animal host to human, followed by
41
human-to-human transmission or direct bat-to-human transmission. The authors also noted that similar
SARS-CoV-like viruses have been identified in several bat species across China. However, they
question whether the HSM was the initial site of spillover (as there were no animals identified from the
market testing positive for SARS-CoV-2) or whether it was a site of amplification. The Lancet report
outlines a possible pathway of a research- or laboratory-associated release of a pathogen – either through
accidental exposure in the field or within a laboratory setting involving a genetically modified virus
during research activities. The Lancet report emphasises that further investigation is required to
investigate both hypotheses and that this will require unbiased, independent, and transparent work led
by international scientific teams supported by governments.
The review by Keusch et al. (2022) covered RNA virus outbreaks, spanning from Marburg virus in
1967 through to SARS-CoV-2, underscoring the recurrent theme of viral origins in avian, bat, and other
mammalian reservoirs and intermediate hosts (Keusch et al., 2022). This brief commentary on
SARS-CoV-2 origins concludes, without presenting original or direct evidence, that the virus is likely
of zoonotic origin, transferred from wildlife to humans via wildlife farming and trade and concludes
that the virus could have evolved to contain a furin cleavage site naturally.
In summary, although both Keusch et al. (2022) and Sachs et al. (2022) papers review published
research, the conclusions were largely opinion-based and did not present any new evidence to support
claims regarding the origins of SARS-CoV-2 (Keusch et al., 2022; Sachs et al.,2022). Similarly, a
commentary by a group of North American scientists also did not introduce novel data but raised
concerns regarding promoting anti-science sentiment and the disproportionate emphasis on a laboratory
origin hypothesis over consideration of a natural spillover (Alwine et al., 2023).
The 2021 review by Holmes provides an overview of the available information regarding the zoonotic
spillover and laboratory origin hypotheses of SARS-CoV-2 (Holmes et al., 2021b). Based on the
available studies and his personal expertise, he described the facts supporting the spillover from bats to
animals and then to humans via an unidentified secondary host. Supporting evidence of early occurrence
in the HSM and wild animals present are explained in detail. The review also offers views regarding
various hypotheses for unnatural origin of SARS-CoV-2 including potential release from a laboratory
but highlights the lack of compelling evidence other than circumstantial elements regarding the work
42
at the WIV, Wuhan CDC and the presence of a furin-cleavage site. His conclusion is that most evidence
points to the HSM as an epicenter, similar to the emergence of SARS-CoV-1 in 2002.
On 2 April 2025, the French National Academy of Medicine published its report entitled ‘From the
Origin of SARS-CoV-2 to the Risks of Zoonoses and Dangerous Virus Handling’, which analysed two
hypotheses: 1) SARS-CoV-2 is a zoonosis and 2) the origin of SARS-CoV-2 is linked to a laboratory
accident. The Academy did not reach any firm conclusions on the subject, which it has taken as a
starting point for reflection on possible recommendations and proposals for action to better anticipate
and react to emerging diseases (Académie Nationale de Médecine, 2025).
While we are aware of several additional reviews, none provided additional scientific evidence and
have not been detailed here further.
Intelligence Reports/Reports from Governments (Summarised in Table 3.B)
In addition to articles in peer-reviewed literature, there have also been reports released by individual
Member State government-related agencies, including from the U.S.A., Germany and China. Seven
reports have been issued by the U.S. government entities and are summarized in Table 3.B. WHO has
requested access to the underlying data these entities used to make their assessments, but, to date, this
access has not been granted; thus SAGO has reviewed what is publicly available.
The U.S. National Intelligence Council (NIC) and the Office of the Director of National Intelligence
(ODNI) issued a report in October 2021 (Office of the Director of National Intelligence, 2021), followed
by an updated report in June 2023 (Office of the Director of National Intelligence, 2023). Both reports
state their findings came from ‘available intelligence reporting and other information’, without stating
the nature of this other information or agreeing to share any of the primary data or intelligence with
SAGO or WHO. The reports include a mix of factual observations, speculative assertions, and calls for
further investigations. Still, neither of the two reports presented any new or conclusive evidence to
support either zoonotic or laboratory origins of SARS-CoV-2.
43
The NIC/ODNI (2021) report stated that four Intelligence Community elements3 assessed with low
confidence that the initial SARS-CoV-2 infection was most likely caused by natural exposure to an
animal infected with SARS-CoV-2 or a close progenitor virus (Office of the Director of National
Intelligence, 2021). One element assesses with moderate confidence that the first human infection with
SARS-CoV-2 most likely was the result of a laboratory-associated incident, probably involving
experimentation, animal handling, or sampling by the Wuhan Institute of Virology. Despite a lack of
consensus between agencies on these two hypotheses, areas of agreement between all agencies
included: that the first known cluster of COVID-19 cases occurred in December 2019 in Wuhan, China;
that the virus was not developed as a bio-weapon; that the virus was not genetically engineered; and
that Chinese officials were not aware of the virus before it emerged (Office of the Director of National
Intelligence, 2021). These findings underscore the complexities and uncertainties surrounding the
origins of COVID-19, highlighting the need for further investigation and international cooperation to
determine the virus' source, close remaining evidence gaps, and align on approaches to obtain
information which might clarify current hypotheses and inferences on origins. Although not citing
specifics, SAGO observes that different US government agencies concluded different probability
rankings for current hypotheses of the origin of SARS-CoV-2. While suggesting areas for additional
research, the assessments highlighted the ongoing disagreement within the intelligence community and
their analysts about the origins of SARS-CoV-2, with some favouring a natural origin caused by
zoonotic transmission and others a laboratory-origin hypothesis.
Members of the United States Senate issued three reports on the origins of SARS-CoV-2: An Analysis
of the Origins of the COVID-19 Pandemic; (Senate Health Education Labor and Pensions Committee
Minority Oversight Staff, 2022), Muddy Waters - The Origins of COVID-19; (Marshall, 2023), and A
Complex and Grave Situation: A Political Chronology of the SARS-CoV-2 Outbreak. (Rubio, 2023).
All three reports contain similar information. The Muddy Waters Group report is the most detailed as
it relates to specific inputs used in the generation of its conclusions. They hint at potential sources that
could lead to a containment breach, including biosafety and biosecurity enhancements at the WIV in
3
Intelligence Community Element means any executive agency or unit thereof determined by the President
under section 2302(a)(2)(C)(ii) of title 5, United States Code, to have as its principal function the conduct of
foreign intelligence or counterintelligence activities.
44
late 2019. However, they stop short of directly suggesting a laboratory breach as the origin of the
COVID-19 pandemic. These reports highlight periodic potential biocontainment and personnel security
weaknesses at the WIV that could potentially result in biocontainment breaches; however, the reports
do not provide any direct evidence. Speculations are made regarding engineering modifications and
upgrades to the laboratories, staff training, but without concrete information and as such they remain
conjecture. Collectively, these reports highlight the critical need for a thorough, unbiased investigation
into the origins of SARS-CoV-2 to enhance global health security and prevent future pandemics.
In late 2024, the After Action Review of the COVID-19 Pandemic: The Lessons Learned and a Path
Forward (Select Subcommittee on the coronavirus pandemic) SSCP report, (Select Committee on the
Coronavirus Pandemic, 2024) was published. While it had a broader mandate than other US government
agency reports, including review of financing and management of the COVID-19 pandemic within the
USA, the report made claims regarding the possibility that SARS-CoV-2 emerged due to a laboratory-
or research-related accident without providing any new evidence or factual scientific evidence to
support such claims. The report provides no new specific data; in fact, most of the relevant section
focuses on the initial development of the “Proximal origin of SARS-CoV-2" Nature Medicine paper
(Andersen et al., 2020). The report focuses on how initial observations on the genomic structure of the
virus identified unique features and speculates as to whether the final statements and conclusions of the
manuscript may have been influenced by other than scientific reasoning.
In response to and countering the arguments of the SSCP report, the US Democrats published Partisan
Probes Over Pandemic Prevention and Preparedness (U.S. House of Representatives Committee on
Oversight and Reform (Democratic Staff), 2024); a report providing a concise review of available
knowledge on potential origins of SARS-CoV-2, concluding that a zoonotic origin and laboratory
accident are both plausible as is a ‘hybrid’ scenario reflecting a mixture of the two, though no new data
to further assess virus origins is provided. A further report by the Central Intelligence Agency has been
cited by media – but is not publicly available and thus has not been reviewed by SAGO.
45
The China White Paper ‘Covid-19 Prevention, Control and Origins Tracing
China’s Actions and Stance’ was released in April 2025 by the State Council Information Office
(State Council Information Office, 2025). It summarizes China’s efforts in containment, cites both
international (joint WHO-China) missions (WHO 2020g; WHO 2021c), and highlights key research
conducted in China on the origins of COVID-19. Key conclusions of the report include that the
government of China considers the work on the origins of COVID-19 in China is finished, which is
not the opinion of SAGO; and that the original source of the infection in China was via the cold chain
from products originating outside China, without citing any new evidence for SAGO to review.
Reports by Civil Groups
The SAGO takes note of reports by civil groups and had been approached by several including
DRASTIC (‘Decentralized Radical Autonomous Search Team Investigating COVID-19') who
investigated the DEFUSE grant proposal by EcoHealth Alliance, previously rejected for funding a
project on bat coronaviruses, which was released publicly following a Freedom of Information Act
request by the organization US Right To Know. SAGO found that these reports did not provide
additional scientific- or intelligence-based data that was not already presented in the above-mentioned
peer-reviewed papers, scientific reviews or reports but include many speculations and theories that are
not backed up by science and were therefore not included in this report.
A report entitled ‘The Most Plausible Origin of SARS-CoV-2’ was also shared with SAGO via email
in late May 2025, summarizing a recent book by Haslam, which proposes a laboratory origin of
SARS-CoV-2 and incriminating specific individual scientists in the USA, Singapore and China based
on the DEFUSE proposal (Haslam and Haslam, 2024). There were several misconceptions,
misinterpretations and speculations in this report, some that SAGO addresses here. While recombinant
chimeric live vaccine technology has been patented by University of North Carolina (UNC), the
DEFUSE proposal did not propose to vaccinate bats using this vaccine. The proposal instead involved
recombinant antigen (synthetic protein) vaccine that would not replicate or spread. Implicated proposals
by NIH involved vaccinating bats with vectored vaccine (Modified Vaccinia Ankara, Vesicular
Stomatitis Virus) which similarly would not spread, and these proposals did not involve coronaviruses.
46
The SHC014 sequence provided by WIV to UNC is not closely related to SARS-CoV-2 but belongs to
another sarbecovirus clade (Menachery et al., 2015). Recombinant vaccine vector genome elements
including HKU3 do not belong to the clade to which SARS-CoV-2 belongs, so that SARS-CoV-2
cannot be derived from this vector. Animal experiments on SARS-CoV-2 in US laboratories do not
allow conclusions regarding geographical origins of SARS-CoV-2. Several additional arguments put
forward in the report and book appear to be caused by misunderstandings, misquotations or confusion
of terms. These affect all elementary motifs of the overall theory put forward.
47
Table 3A: Published Scientific Reviews
The Lancet Commission on lessons for the future from the COVID-19 pandemic
Sachs et al. Lancet Commission. Published 2022. (Sachs et al., 2022)
• No new evidence was presented for either hypothesis: the virus emerged as a zoonotic spillover from wildlife or a farm animal, possibly through
a wet market, in a location that is still undetermined; or the virus emerged from a research-related incident, during the field collection of viruses
or through a laboratory-associated escape.
• The zoonotic spillover theory was presented in detail with potential natural spillover from a bat reservoir, via intermediate animal host to
human, followed by human-to-human transmission or direct bat to human transmission.
• SARS-CoV-2 is thought to derive from a bat SARS-CoV-related coronavirus with a furin cleavage site that enhances the capacity of the virus
to infect human cells.
• Questions the suggestion that the HSM was the primary site of spillover (given that no animals from the market tested positive for SARS-CoV-2)
or if it served as a secondary outbreak location and site of amplification.
• Since 2006, following the emergence of SARS, furin cleavage sites have also been the subject of laboratory manipulation, including their
insertion into coronavirus spike proteins.
• The presence of the furin cleavage site in SARS-CoV-2 therefore does not by itself identify the proximal origin of the virus, whether natural or
laboratory.
• WHO, governments, and the scientific community should intensify the search for the origins of SARS-CoV-2, investigating both a possible
zoonotic origin and a possible research-associated origin. The search for origins requires unbiased, independent, transparent, and rigorous work
by international teams in virology, epidemiology, bioinformatics, and other related fields.
Pandemic origins and a One Health approach to preparedness and prevention: Solutions based on SARS-CoV-2 and other RNA viruses.
PNAS.
Keusch, Gerald T. et al. Published 2022. (Keusch et al., 2022)
• Examined RNA virus outbreaks to highlight the recurring pattern of viral origins, with pathogens emerging from avian, bat, and other
mammalian reservoirs, often involving intermediate hosts, in previous outbreaks.
• The increasing scientific evidence concerning the origins of Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) is most
consistent with a zoonotic origin and a spillover pathway from wildlife to people via wildlife farming and the wildlife trade.
• This builds on the accepted spillover theory of SARS-CoV-1 from the masked palm civet (Paguma larvata) and perhaps raccoon dogs (Nyctereutes
procyonoides) linked to a live animal market in Guangdong, China which led to the SARS outbreak in 2003.
48
The Emergence and Evolution of SARS-CoV-2.
Annual Review of Virology (Holmes et al., 2021b)
• The review provides an overview of the diversity, hosts and geographical distributions of Sarbecoviruses pointing to a distribution of SARS-
CoV-1 and SARS-CoV-2-related sequences in southeastern Asia. Rhinolophus bats have been the host from which most closely related viral
sequences were recovered. Sarbecovirus origins and evolution from pangolins are also discussed in relation to SARS-CoV-2.
• The review summarizes the information available regarding the HSM in relation to early occurrence and detection of SARS-CoV-2. A
description of the geolocation studies of early COVID-19 patients is discussed, supporting the market as an epicenter or amplifying location,
along with the documented presence of potential intermediate hosts such as wild mammals or farmed animals (presence documented by picture,
metagenomic analysis and documentaries) permissive for an animal-human interface which could drive “cross species transmission”.
• The review offers a summary table describing the various hypotheses for unnatural origin of SARS-CoV-2 including potential release from a
laboratory but highlights the lack of evidence other than circumstantial elements regarding the WIV, Wuhan CDC and the presence of a furin-
cleavage site. The author also cites personal communications that one researcher - implicated in some theories as “the researcher” infected with
SARS COV-2 - tested negative by PCR and serology for COVID-19 in 2020.
• As an example of the evolution of SARS-CoV-2, the Omicron variant’s possible origin is also described such as either undetected spreading,
evolution in an animal host or within a chronically infected, likely immunosuppressed individual.
49
Table 3B: Government Reports/Assessments
1.Updated assessment on COVID-19 origins
National Intelligence Council (NIC).
Published 2021. (Office of the Director of National Intelligence, 2021)
• Four Intelligence Community (IC) elements and the National Intelligence Council assess with low confidence that the initial SARS-CoV-2
infection was most likely caused by natural exposure to an animal infected with it or a close progenitor virus, a virus that probably would be
more than 99 percent similar to SARS-CoV-2.
• Emergence Timeline: The NIC assesses that SARS-CoV-2, the virus responsible for COVID-19, probably emerged and infected humans
through an initial small-scale exposure that occurred no later than November 2019, with the first known cluster of COVID-19 cases arising in
Wuhan, China, in December 2019.
• Natural Zoonotic Origin: Four intelligence agencies, along with the National Intelligence Council, assessed with low confidence that the
initial SARS-CoV-2 infection was most likely caused by natural exposure to an infected animal or a close progenitor virus.
• Laboratory Incident Hypothesis: One agency assessed with moderate confidence that the first human infection was most likely the result of
a laboratory incident, likely involving experimentation, animal handling, or sampling in the Wuhan Institute of Virology.
• Uncertainty and Intelligence Gaps: Three other agencies remained unable to agree on either hypothesis without additional evidence, with
some favouring natural origin, others a laboratory origin, and some seeing the hypotheses as equally likely. Variations in analytical views were
largely a result of differences in the way agencies have studied intelligence reports and scientific publications, as well as intelligence and
scientific gaps.
• China's Cooperation: Criticizing governmental authorities for continuing to hinder the global investigation and refusing to share information.
It also stated that the Chinese government's actions reflected its own uncertainty about where an investigation could lead, as well as its
frustrations that the international community was using the issue to exert political pressure on China. Cooperation with China is needed to reach
a conclusive assessment on the origins of the disease
• These findings underscore the complexities and uncertainties surrounding the origins of COVID-19, highlighting the need for further
investigation and international cooperation to determine the virus' source.
• The report identifies knowledge gaps, and approaches to obtain information which might clarify hypotheses and inferences on origins.
• Although not citing specifics, SAGO observes that different US government agencies came to different ranking of hypotheses for the origin of
SARS-CoV-2 and COVID-19.
2.Potential links between the Wuhan Institute of Virology and the origin of the COVID-19 Pandemic
Office of the Director of National Intelligence - (ODNI). National Intelligence Officer for Weapons of Mass Destruction and Proliferation and
coordinated with the IC. Published 2023. (Office of the Director of National Intelligence, 2023)
50
• Almost all U.S. Intelligence Community (IC) agencies concur that SARS-CoV-2 was not genetically engineered. Most agencies assess that
SARS-CoV-2 was not laboratory-adapted; some are unable to decide. All IC agencies assess that SARS-CoV-2 was not developed as a
biological weapon.
• U.S. IC has found no direct evidence of a "biosafety incident" or of the pre-pandemic presence of the virus that causes COVID-19 at a laboratory
in Wuhan, China.
• The National Intelligence Council and four other IC agencies assess that the initial human infection with SARS-CoV-2 most likely was caused
by natural exposure to an infected animal that carried SARS-CoV-2 or a close progenitor, a virus that probably would be more than 99 percent
similar to SARS-CoV-2.
• The Central Intelligence Agency and another agency remain unable to determine the precise origin of the COVID-19 pandemic, as both
hypotheses rely on significant assumptions or face challenges with conflicting reporting.
• The Department of Energy and the Federal Bureau of Investigation assess that a laboratory-associated incident was the most likely cause of the
first human infection with SARS-CoV-2, although for different reasons.
3.An Analysis of the Origins of the COVID-19 Pandemic Interim Report
Senate Committee on Health Education, Labor and Pensions (HELP). Published 2022.
(Senate Health Education Labor and Pensions Committee Minority Oversight Staff, 2022)
• Reviews publicly available information to assess two prevailing theories regarding the origin of SARS-CoV-2:
o Natural Zoonotic Origin: The virus emerged from an animal reservoir, such as bats or other wildlife, and transmitted to humans
through an intermediate host.
o Research-Related Incident: The virus accidentally leaked from a laboratory, such as the Wuhan Institute of Virology, due to
inadequate safety protocols.
• The report emphasizes the need for a comprehensive, transparent investigation to determine the virus' origin and to inform future pandemic
preparedness.
4.Origins of COVID-19 report
Muddy Waters Group (MWG). Published 2023 (Marshall, 2023)
• Describes the complexities and uncertainties surrounding the origins of SARS-CoV-2.
• It examines various hypotheses, including zoonotic spillover and laboratory-related incidents, and highlights the challenges in obtaining conclusive
evidence.
• The report underscores the importance of international cooperation and transparency in scientific research to uncover the true origins of the virus.
5.A Complex and Grave Situation. A political chronology of the SARS-CoV-2 outbreak
Rubio State Senate. Published 2023. (Rubio, 2023)
• This document provides a chronological account of the political responses to the SARS-CoV-2 outbreak, both within the United States and
internationally.
51
• It outlines key decisions, policy shifts, and diplomatic interactions that shaped the global response to the pandemic.
• The report offers insights into the interplay between political considerations and public health measures during the early stages of the outbreak.
6.After Action Review of the COVID-19 Pandemic: The lessons learned and a path forward.
Select subcommittee on the coronavirus pandemic. Published 2024. (Pandemic, 2024)
• Notes the possibility that COVID-19 emerged due to a laboratory- or research-related accident is not a conspiracy theory.
• It references a Fact Sheet released by the State Department in 2021 – which claims that the US government had reason to believe there were
several researchers inside the WIV who became sick with symptoms in line with common seasonal illness or COVID-19.
• It also references the ODNI report which makes reference to WIV activities on SARS-like coronaviruses and its involvement with the Chinese
military. It also states that the ODNI report claims “some WIV researchers probably did not use adequate biosafety procedures…”. It
references the DOE and FBI who made similar assessments that COVID-19 was likely the result of a lab incident (FBI with moderate
confidence and DOE with low confidence.
• proposes that Ecohealth Alliance facilitated gain-of-function research in WIV and were unable to acquire copies of WIV notebooks in 2021
to understand the extent of recombinant bat-coronavirus virus work being done at WIV, and absence of receipt of that information.
7. Partisan Probes Over Pandemic Prevention and Preparedness – Democratic Final Report
Published 2024. (U.S. House of Representatives Committee on Oversight and Reform, Democratic Staff, 2024).)
• Democratic Party opinion based on the above Select Subcommittee Report.
• ‘After hearings etc., … the Select Subcommittee remains in the same position in which it started: the origins of COVID-19 are unknown. A
zoonotic origin and lab accident are both plausible, as is a “hybrid” scenario reflecting a mixture of the two’.
• Does not add any new evidence.
• Questions accusation by Select Subcommittee that NIAID director or EcoHealth Alliance ‘created’ SARS-CoV-2.
52
Discussion
Prior to the emergence of SARS-CoV-2, all known human coronaviruses that have emerged in past
decades are believed to have originated in bats or rodents and spilled over to humans through an
intermediate animal host (Corman et al., 2018; Mittal et al., 2020). SARS-CoV-1 (2003), for instance,
has a precursor virus in bats, with masked palm civets and possibly raccoon dogs acting as intermediate
hosts (Mittal et al., 2020). For the Middle East Respiratory Syndrome Coronavirus (MERS-CoV; 2012),
dromedary camels have been identified as the intermediate host (Reusken et al., 2013; Mohd et al.,
2016). While the initial SARS-CoV-2 strain is most closely related to the Laos BANAL-52 bat strains,
an intermediate host has yet to be identified.
SAGO has reviewed available published and unpublished scientific evidence related to the origin of
SARS-CoV-2, received presentations by scientists from China and elsewhere (institutions listed in
methods section and acknowledgements); the joint international WHO and China teams’ mission report
from 2021 and had discussions with researchers and other groups conducting relevant work as outlined
in this report. SAGO applied the Global Framework for investigation of the origins of novel pathogens
(WHO, 2024a) to thoroughly assess the available scientific information covering the key elements for
investigation of the emergence of novel pathogens including 1) early investigations around the first
human cases and the HSM; 2) early human epidemiology and surveillance data globally, including in
the months preceding 1 January 2020; 3) investigations at the animal/human interface including
precursors strains from bats and potential susceptible hosts, 4) environmental surveillance data, 5)
genomic analysis to understand the genome structure and evolution as well as 6) laboratory biosafety
and biosecurity at laboratories where the initial cases were reported in Wuhan China.
SAGO has also reviewed scientific and non-scientific publications including reports by independent
bodies and met with journalists who presented unpublished information from their work. SAGO
reviewed this information and included what was deemed scientifically and factually relevant in this
assessment (Keusch et al., 2022; Sachs et al., 2022; Senate Health Education Labor and Pensions
Committee Minority Oversight Staff, 2022; Marshall, 2023; Rubio 2023; Office of the Director of
53
National Intelligence, 2021; Office of the Director of National Intelligence, 2023). The WHO
Secretariat and SAGO members searched for and reviewed reviews, evidence and opinion pieces from
January 2020 and up to April 2025. Any which did not provide any novel data and/or information were
therefore not included in SAGO’s review. Although evidence is still missing, making it difficult to
conclude how exactly the SARS-CoV-2 virus spilled over into the human population, assessing
currently available and accessible data affords the scientific community a better understanding about
the origins of SARS-CoV-2.
To summarize, the evidence available for analysis remains the following:
1) Despite screening of animal and human samples using molecular and serologic testing from samples
collected in the second half of 2019 in a number of countries globally, no animal or human clinical
samples positive for SARS-CoV-2 have been identified and/or verified prior to December 2019;
suggesting that SARS-CoV-2 did not circulate widely in humans prior to December 2019. It is possible
that there were earlier human cases prior to December 2019, but currently there is no available evidence
to confirm this. Serological screening of 43,850 blood bank samples from Wuhan prior to December
2019 yielded no reported positives suggesting the virus didn’t circulate widely in the city prior to the
detected cases on 1 December 2019, current data supports that the first cases occurred in Wuhan China
in early December 2019.
Reports of molecular screening and genetic sequencing of wastewater samples and serological studies
from human clinical samples from Italy, France and Brazil proposed that the virus may have circulated
undetected as early as November 2019 in some countries. However, these reports have not been verified
by external laboratories. The validity of the study from Italy was compromised by several factors: 1.
the outcomes not exceeding the expected rate of false-positive samples occurring by chance 2. the lack
of double IgM and IgG specimens as would have been expected at least in some of the cases 3. lack of
negative control samples from previous years. A lack of clinical cases identified prior to early December
or molecular confirmation suggests that circulation may have been at low levels and sporadic cases
could have been asymptomatic or sub-clinical and, therefore, not severe enough to seek medical care
nor require hospitalization or resulting in secondary infections. With the available information, it is
54
difficult to verify if earlier circulation, prior to December 2019, was taking place. Further investigations
from stored respiratory disease surveillance samples, wastewater or clinical specimens in China and
globally should continue to be tested to determine if there was indeed circulation or if any undetected
outbreaks occurred before December 2019.
2) Although not all of the reported cases in December 2019 had a direct link to the HSM, analyses of
available geospatial data, sequence data, clinical and environmental samples suggests that many of
those without a reported direct link lived in the vicinity of the market, indicating that most individuals
that tested positive had chances of contact with animals/animal products or visitors from the market
(Worobey et al., 2022a). This supports the hypothesis that the market played an important role, either
due to spillover from animals, though possibly not the first spillover events, or as an amplification site
for SARS-CoV-2 from infected humans present at the market (Temmam et al., 2022).
With currently available information, questions remain on exactly when and where a) the first cases
occurred and b) onward transmission into the human population began. There are considerable gaps in
our understanding of the testing done in humans working at markets in and around Wuhan, at the farms
or along trade routes for the animals that were sold at the HSM and/or at farms raising animals known
to be susceptible to SARS-CoV-2 infection. This makes it currently not possible to determine whether
spillover of SARS-CoV-2 occurred upstream from source farms providing animals to the HSM or at
the market itself. The HSM was a site for amplification, which allowed the virus to spread further, but
it is not possible to determine if the first infections occurred at the HSM. Further sharing of data on
early investigations, if they have taken place is critical, as is all sequencing data of these early detections
to determine the genetic distance to the original SARS-CoV-2 strains reported from Wuhan.
3) Analysis of available genomes provides evidence of two separate introductions of SARS-CoV-2
virus lineages - that led to the development of a sustained epidemic in humans has also been found after
conducting analyses from environmental samples collected from the HSM in early 2020. (Crits-
Christoph et al., 2024; Liu et al., 2023) These findings and evolutionary analyses suggest that these
introductions occurred after November 2019 (Worobey et al., 2022a; Pekar et al., 2022).
55
4) Two other unique features of the SARS-CoV-2 genome have been the focus of debate on the origin
of SARS-CoV-2. As described in the genomics investigations section of this report, evidence around
the evolution of the virus suggests that these features likely developed through natural evolution in
susceptible animals and humans due to a propensity for recombination and accumulation of mutations
associated with coronaviruses, including SARS-CoV-2. Furin cleavage sites occur in other human
coronaviruses and had been previously identified in nature, for example in animal-associated
merbecoviruses. This suggests that it could also be acquired in sarbecoviruses through natural
recombination events between related sarbecoviruses in humans or susceptible animals. Based on our
knowledge on coronavirus evolution and biology, this and other features of SARS-CoV-2 are readily
explained by natural evolution and provide no support to theories of a man-made origin (Keusch et al.,
2022; Sachs et al., 2022; Senate Health Education Labor and Pensions Committee Minority Oversight
Staff, 2022; Marshall, 2023; Rubio, 2023; Office of the Director of National Intelligence, 2021; Office
of the Director of National Intelligence, 2023). However, the latter is also not refuted by biological data.
5) It has been reported to SAGO and WHO that no stored samples from animals in China taken before
the first identified human cases of COVID-19 (January 2020) were SARS-CoV-2-positive (WHO,
2022). This has not been independently verified by SAGO. However, it seems unlikely that there have
been no animal SARS-CoV-2 reverse zoonotic infections in China since the onset of the COVID-19
pandemic (aside from Syrian hamsters in Hong Kong Special Administrative Region), considering the
many susceptible species present there, the reverse zoonoses events reported in various susceptible
species around the world, and the possibility of exposure to potentially infected animals at source farms
and the HSM. Despite some testing of the environment and animals sampled from the HSM, there was
a limited number of susceptible species included in this testing, thus limiting the ability to make
definitive conclusions. It is likely that many animals had already been removed due to public health
measures imposed on 1 January 2020, when the market was shut down and disinfected; therefore, they
were not traced for sampling. It remains the recommendation of SAGO that investigation of animals,
animal vendors and source farms related to the HSM and susceptible species across Southeast Asia
should have been conducted, and that if these investigations have already taken place, that these results
56
be shared (Liu et al., 2023). There would be value in tracing the movements of these animals from
source to market, even 5 years later.
Currently, the most compelling evidence of a possible spillover from animals to humans comes from
the independent metagenomic data analysis, which confirmed the presence of mitochondrial DNA of
animals known to be susceptible in stalls at the HSM, and SARS-CoV-2 positive environmental swabs
from the same stalls. The data confirms that these animals were present before the market was closed
on 1 January 2020 and may have been a source for human infection. These species should be a focus of
ongoing investigations into the identification of the intermediate host(s).
6) SAGO worked closely with the WHO Technical Advisory Group on Biosafety and Biosecurity
(TAG-B), which provides expert advice and scientific and technical recommendations for evidence-
based biosafety and biosecurity control strategies to improve the safety of pathogen laboratories
worldwide (WHO, 2020a). Together, SAGO and TAG-B identified and outlined the critical areas for
investigating potential breaches in biosafety and biosecurity to ensure a comprehensive assessment of
risks and vulnerabilities in laboratory settings.
At the present, it is not possible to assess the possibility of an incident occurring in laboratories in
Wuhan as SAGO has not had the opportunity to formally examine the biosafety and biosecurity
protocols and measures that were in place, the activities conducted in those facilities, or the health status
of staff from late 2019. SAGO notes that no evidence has been presented, other than speculation from
scientific or intelligence reports, that supports a laboratory-related incident causing the spread of
SARS-CoV-2 into the human population. Without the requested information, this hypothesis can
however not be ruled out.
Conclusion
More than five and a half years have passed since the first reported cases of SARS-CoV-2 infection
were reported in Wuhan, China in December 2019. Although evidence exists that has improved our
understanding of the early and subsequent evolution of the virus in humans and animals, significant
57
data gaps remain which preclude SAGO from concluding with certainty how SARS-CoV-2 initially
entered the human population.
Throughout the development of this independent assessment, it may be obvious to state that SAGO has
only been able to analyze evidence made available to them and the public. However, SAGO and WHO
are aware that more data exists. Some examples of this include requests for more information including:
a) the sharing of more than 500 sequences from individuals with COVID-19 early in the
pandemic; (China National Center for Bioinformation, 2022).
b) more detailed information on the sources, locations, sampling and testing methods of animals
sold at the HSM and other wet markets in Wuhan, including upstream farming or illegal trade;
and
c) information on research and field activities in laboratories in Wuhan, including staff health
records, biosafety and biosecurity information of the Wuhan Institute of Virology, and the
Wuhan China CDC laboratory.
The weight of available evidence reviewed by SAGO suggests zoonotic spillover of SARS-CoV-2 into
the human population, either directly from bats or through an intermediate host. However, SAGO
cannot conclude with certainty where and when this occurred, nor if the HSM was indeed the first
instance of spillover into the human population, or the site of further spillover and amplification.
Susceptible infected animals (or animal products) could have acted as reservoirs and therefore exposed
humans through different routes: (a) before the infected animals or humans arrived at the HSM, or (b)
once the infected animal or animal product arrived at the HSM. However, irrespective of the precise
spillover event or events, the HSM appears to be location for amplification of infection in humans
leading to widespread transmission to surrounding areas in China, and eventually to other countries.
Evidence for widespread infections or cases in any other countries prior to December 2019 is lacking,
as well as evidence to support the cold chain hypothesis. Information and evidence is also lacking to
assess the possibility of a laboratory origin - either the evidence is not available or has not been provided
to the scientific community. As a result, SAGO has been unable to adequately assess this route for
58
human infection and therefore is not in a position to rule this out as a possibility. Hypotheses submitted
to the SAGO or available in the public domain on intentional manipulation of the virus however, are
not supported by accurate science, and not currently considered as the likely source.
Nevertheless, based on the recommendations in SAGO’s preliminary report on COVID-19 (WHO,
2022), outcomes from the March 2021 WHO-convened global mission (WHO, 2021) and recent
findings from scientific evidence related to SARS-CoV-2 origins, the scientific investigations and
studies recommended in Table 4 remain to be conducted, in order for the scientific community to
conclude with more certainty the origins of SARS-CoV-2.
The COVID-19 pandemic has caused so much suffering and devastation globally for the world not to
know exactly how this pandemic started. SAGO urges China together with the global scientific
community to prioritize further work on understanding the origins COVID-19 and for all countries to
comprehensively study future emergences of unknown pathogens.
SAGO remains committed to science and will continue to evaluate any and all new sound scientific
evidence and data as it is made available through public or private sources to clarify the origins of
SARS-CoV-2. If provided with reliable evidence, SAGO is available to evaluate all possibilities to
revise this report.
59
Table 4. Recommended investigations into the origins of SARS-CoV-2: The following are recommended studies that are outstanding from
previous reports and the SAGO considers them to still be pertinent.
Aim Outstanding recommended studies (what is still feasible) Status
(to the best of our knowledge – has not
been done)
Identification of potential Wastewater and clinical samples surveillance, from influenza-like illness (ILI) and Not conducted or if done not made
previously unrecognized Severe Acute Respiratory Infections (SARI) and polio surveillance from East and publicly available. Still feasible where
COVID-19 cases prior to Southeast Asia from September to November/December 2019 that may identify archived samples exist in research and
December 2019 earlier cases with an expanded case definition, in order to capture milder cases and public health institutions.
younger individuals.
Investigation of animals, Focused serological and genetic testing and increased surveillance of animals Some wildlife surveillance was conducted
animal vendors and and/or wildlife associated with the HSM in live animal markets and upstream by Chinese researchers, but the sampling
source farms related to supply farms are essential to monitor high-risk potential host species. Testing sick strategy and methods were unclear, as the
the HSM and susceptible or dead animals, particularly those from susceptible species, and conducting numbers of samples/species tested, which
species across Southeast sequencing to monitor virus evolution is recommended. (EFSA Panel on Animal were limited, did not include sampling
Asia Health and Welfare et al., 2023) from source farms, targeted wildlife value
chains or all appropriate susceptible
species.
Mammalian species susceptibility to SARS-CoV-2 and potentially levels of virus If this data or stored samples are
shedding, including raccoon dogs, civets, bamboo rats, Malayan porcupines, and available from research or veterinary labs
hedgehogs, as well as minks and bats throughout Southern China and South-East this may still be carried out. Testing of
Asia, can shed light on the animal trade networks that may have led to the current samples or animals should be
emergence of SARS-CoV-2 as previously recommended. (WHO, 2022) prioritized to prevent future spill over
events even if it is unlikely to yield the
Archived samples from prior to Jan 2020 should be traced from research, source of the COVID19 pandemic.
veterinary or public health laboratories, and other sources to be tested to identify
the presence of SARS-CoV-2 infection prior to December 2019.
Systematic random sampling of wildlife farms, hunters or animal traders in and
around the Wuhan region is still outstanding. There is a need for more
60
information, particularly from source farms trading animals to wet markets in
Hubei Province, China prior to Jan 2020.
Continued syndromic and genomic surveillance in humans and animals in the East Not conducted or if done not publicly
and Southeast Asia region may detect continued circulation of early human strains available; only partial sequences of bat
in animal reservoirs or emerging variants of concern. Specifically, those who enter SARS-CoV-like strains are available.
caves and communities in the vicinity where precursor strains circulate including
RaTG13 in China and Banal-52 strain in Lao People’s Democratic Republic and
recent SARS-CoV-like bat viruses (that can infect human cells). In addition,
SARS-CoV-like viruses detected in bats by Southeast Asian researchers that had
not been sequenced yet should be subjected to whole genome sequencing.
Biosafety and Biosecurity An independent review of the laboratories in the proximity of the HSM should be Not conducted despite numerous
investigations conducted, including the research conducted in the years prior to the outbreak of advocacy attempts.
SARS-CoV-2, the biosafety and biosecurity practices and procedures in place at
the end of 2019, and the health of staff before and after the recognition of the
outbreak. Independent international investigations and/or follow-up of any
suggested evidence from laboratories in other parts of the world that worked on
coronaviruses should also be investigated for SARS-CoV-2 activities prior to
December 2019.
.
61
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Annex
Annex 1. Table 1. Animal species naturally infected (RNA detection) by SARS-CoV-2
(Reference: Food and Agriculture Organization of the United Nations, 2023)
Year reported &
Animal species Scientific name Country/Territory Site number of epi
units affected 4
Domestic cat Felis catus Argentina, Belgium, Brazil, Household 2020 (76)
Canada, Chile, Croatia, Ecuador, 2021 (94)
Egypt, Estonia, France, Finland, 2022 (31)
Germany, Greece, Hong Kong 2023 (2)
SAR., Hungary, Iran, Italy, Japan,
Latvia, Mexico, Netherlands,
Nigeria, Portugal, Republic of
Korea, Russia, Spain,
Switzerland, Thailand, United
Kingdom of Great Britain and
Northern Ireland, United States of
America, Uruguay
Domestic Dog Canis lupus Argentina, Bosnia and Household 2020 (76)
familiaris Herzegovina, Brazil, Canada, 2021 (76)
Chile, Colombia, Croatia, 2022 (93)
Denmark, Ecuador, Egypt, 2023 (7)
Finland, France, Hong Kong
SAR, India, Italy, Japan, Jersey,
Mexico, Myanmar, Netherlands,
Nigeria, Portugal, Republic of
Korea, Spain, Switzerland,
Thailand, the United Kingdom of
Great Britain and Northern
Ireland, United States of America,
Uruguay
Domestic Neovison vison Bulgaria, Canada, Denmark, Farm 2020 (349)
American Mink France, Greece, Italy, Latvia, 2021 (32)
Lithuania, Netherland, Poland, 2022 (2)
Spain, Sweden 2023 (1)
Domestic Ferret Mustela furo Slovenia, United States of Household 2020 (1)
America 2021 (1)
2024 (1)
Wild American Neovison vison Spain, United States of America Free range 2020 (no data)
Mink 2021 (2)
Western lowland Gorilla gorilla United States of America, Spain, Zoo 2021 (12)
Gorilla gorilla the Netherlands, Brazil 2022 (5)
4
individual animal cases or production or marketing units such as farms or markets
72
Year reported &
Animal species Scientific name Country/Territory Site number of epi
units affected 4
White-tailed deer Odocoileus Canada, United States of America Natural Park 2021 (350)
virginianus Wild habitat (hunted) 2022 (625)
2023 (1)
2024 (7)
Binturong Arctictis binturong United States of America Zoo 2021 (1)
Coatimundi Nasua nasua Brazil, United States of America Zoo 2021 (3)
Urban Park
Fishing cat Prionailurus United States of America Zoo 2021 (1)
viverrinus
Tiger Panthera tigris Argentina, Denmark, Indonesia Animal sanctuary 2020 (1)
Sweden, United Kingdom of Zoo 2021 (24)
Great Britain and Northern Wild animal exhibitor 2022 (4)
Ireland, United States of America facility 2023 (1)
Lion Panthera leo Croatia, Colombia, Estonia, Zoo 2020 (2)
Japan, the Netherlands, Puerto 2021 (26)
Rico, Singapore, South Africa, 2022 (3)
Spain, Sweden, United States of 2023 (1)
America
Puma Puma concolor Argentina, South Africa, United Wild animal exhibitor 2020 (2)
States of America facility 2021 (1)
Rescue center
Snow Leopard Panthera uncia United States of America Zoo 2020 (3)
2021 (2)
Indian Leopard Panthera pardus India Free range 2021 (1)
fusca
Canada Lynx Lynx canadensis United States of America Zoo 2021 (1)
Spotted hyenas Crocuta crocuta United States of America Zoo 2021 (2)
Asian small- Aonyx cinereus United States of America Aquarium 2021 (9)
clawed otters Zoo
Hamster Mesocricetus Hong Kong SAR, China Pet shop 2022 (2)
auratus Warehouse of pets
Wild Eurasian Lutra lutra Spain Free range 2021 (1)
River Otter
Hippopotamus Hippopotamus Belgium, Viet Nam Zoo 2021 (1)
amphibius 2022 (2)
Unspecified
Black-Tailed Mico melanurus Brazil Free range 2022 (1)
Marmoset
73
Year reported &
Animal species Scientific name Country/Territory Site number of epi
units affected 4
Mule deer Odocoileus United States of America Natural Park 2022 (1)
hemionus 2023 (2)
Antillean Trichechus Brazil Captive 2020 (2)
manatees manatus manatus
Giant anteater Myrmecophaga Brazil Free range 2022 (1)
tridactyla
Mandrill Mandrillus sphinx United States of America Zoo 2022 (1)
Monkey Squirrel Saimiri sciureus United States of America Zoo 2022 (1)
Red fox Vulpes vulpes Switzerland Zoo 2022 (1)
Cattle Unspecified India, Nigeria, Republic of Korea Animal-rearing pockets 2021/2022 (32)
Unspecified 2023 (1)
Buffalo Unspecified India Animal-rearing pockets 2021/2022 (13)
Goat Unspecified Nigeria Unspecified 2021/2022 (46)
Capra hircus Republic of Korea 2023 (1)
coreanae
Black-and brown Ateles fusciceps Ecuador Captive 2022 (20)
headed Spider
Monkey
Common woolly Lagothrix Ecuador Captive 2022 (1)
monkey lagothricha
White rhinoceros Ceratotherium Senegal Natural reserve 2023 (1)
simum
Ducka Unspecified Nigeria Households and 2021/2022 (2)
backyard farms
Chickena Unspecified Nigeria Households and 2021/2022 (10)
backyard farms
Turkeya Unspecified Nigeria Households and 2021/2022 (1)
backyard farms
Sheep Unspecified Nigeria Households and 2021/2022 (50)
backyard farms
Pig Unspecified Nigeria Households and 2021/2022 (4)
backyard farms
Lizard Agama agama Nigeria Households and 2021/2022 (19)
backyard farms
Eurasian beaver Castor fiber Mongolia Farm 2021 (1)
74
Year reported &
Animal species Scientific name Country/Territory Site number of epi
units affected 4
White-fronted Cebus unicolor Peru Captive 2022/2023 (9)b
capuchin
House mouse Mus musculus Mexico Urban 2020 (4)
Brown rat Rattus norvegicus Mexico Urban 2020 (3)
Big hairy Chaetophractus Argentina Captive 2022 (3)
armadillo villosus
Pantanal cat Leopardus Brazil Captive 2021 (1)
braccatus
Gray brocket Subulo Brazil Captive 2022 (1)
gouazoubira
Red deer Cervus elaphus Brazil Captive 2022 (1)
Manned wolf Chrysocyon Brazil Captive 2022 (2)
brachyurus
European fallow Dama dama Brazil Captive 2022 (1)
deer
Eastern deer Peromyscus United States of America Natural habitat study 2023 (8)
mouse maniculatus
Raccoon Procyon lotor United States of America Wildlife center and 2023 (4)
natural habitat
Eastern cottontail Sylvilagus United States of America Wildlife center 2023 (3)
floridanus
Eastern red bat Lasiurus borealis United States of America Natural habitat 2023 (1)
Groundhog Marmota monax United States of America Wildlife center 2023 (3)
Virginia opossum Didelphis United States of America Wildlife center and 2022 (1)
virginiana natural habitat 2023 (3)
75
Annex 1. Table 2. Animal species susceptibility to SARS-CoV-2 based on experimental
infection studies
(Reference: Food and Agriculture Organization of the United Nations. (2023)
Animal species Scientific name (wild animals) Susceptibility Transmission5
Raccoon dogs (reference) Nyctereutes procyonoides Yes Yes
Red Fox (reference) Vulpes vulpes Yes Not specified
Coyotes
Canis latrans No -
(reference)
Deer mice (reference) Peromyscus maniculatus Yes Yes
Bank voles (reference) Myodes glareolus Yes No
Bushy-tailed woodrats (reference) Neotoma cinerea Yes Not specified
Laboratory BALB/c mice
Yes Yes
(reference)
White-tailed deer (reference) Odocoileus virginianus Yes Yes
Ferret (reference) Mustela furo Yes Yes
Egyptian fruit bat Rousettus aegyptiacus Yes Yes
Striped skunks (reference) Mephitis mephitis Yes Not specified
Zebra fish (reference) Danio rerio Yes Not specified
Zebra mussel (reference1)
Dreissena polymorpha Yes Not specified
(reference2)
Syrian hamsters Mesocricetus auratus Yes Yes
Tree shrews (reference1)
Tupaia belangeri chinensis Yes Not specified
(reference2)
Rhesus macaques (reference) Macaca mulatta Yes Not specified
The crab-eating macaque
Macaca fascicularis Yes Not specified
(reference)
Baboons (reference) Papio hamadryas Yes Not specified
Common marmosets (reference) Callithrix jacchus Yes Not specified
Cynomolgus macaques (reference) Macaca fascicularis Yes Not specified
African green monkeys (reference) Chlorocebus aethiops Not susceptible Not specified
Aedes aegypti, Aedes. albopictus,
Mosquitoes
Culex tarsalis and Culex Not susceptible -
(reference1) (reference2)
quinquefasciatus
76
Midge (reference) Culicoides sonorensis Not susceptible -
Chicken – Duck – Geese – Turkey
- Not susceptible -
– Quail and Pigeon (reference)
Pig (reference1) (reference2) Yes (Low
- No
(reference3) susceptibility)
Cattle (reference1) (reference2) Yes (Low
- No
(reference3) susceptibility)
Horse (reference) - No -
Yes (Low
Sheep (reference) - No1
susceptibility)
Yes (Low
Goat (reference1) (reference2) - Not specified
susceptibility)
Alpaca (reference) - No -
Rabbit (reference) - Yes Not specified
Cat (reference) - Yes Yes
Yes (Low
Dog (reference) - No
susceptibility)
Sprague Dawley rats (reference) Rattus norvegicus Yes Not specified
Yes (ancestral
virus)
Elk (reference1) (reference2) Cervus canadensis (Low No
susceptibility to
Delta VOC)
Mule deer (reference) Odocoileus hemionus Yes Yes
Mexican free-tailed bats
Tadarida brasiliensis Yes No
(reference)
Little brown bats (reference) Myotis lucifugus No
5
to co-housed animals of same species
77
END OF REPORT.
78
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