Vaccine Safety (GAO-21-342SP)
Summary
A GAO Science & Tech Spotlight on vaccine safety, GAO-21-342SP, dated February 2021, from GAO's Science, Technology Assessment, and Analytics team. It explains that a vaccine is generally considered safe when the benefits of protecting an individual from disease outweigh the risks from potential side effects, the most common being swelling at the injection site, fever and aches. It describes how developers assess safety from early research through laboratory and animal testing and after a vaccine is in use. It notes that safety information from preclinical trials of mRNA flu vaccine candidates in 2017 allowed for the acceleration of mRNA COVID-19 vaccine development.
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Science, Technology Assessment,
FEBRUARY 2021
and Analytics
WHY THIS MATTERS
Safe vaccines are critical to fighting diseases, from
polio to COVID-19. Research shows that the protection
SCIENCE & TECH SPOTLIGHT: provided by U.S. licensed vaccines outweighs their
VACCINE SAFETY
potential risks. However, misinformation and unjustified
safety concerns can cause people to delay or refuse
vaccination, which may increase preventable deaths
and prolong negative social and economic impacts.
/// THE SCIENCE What is known? Vaccine developers assess safety from early research,
through laboratory and animal testing, and even after the vaccine is in use
What is it? A vaccine is generally considered safe when the benefits of (fig. 2). Researchers may rely on previous studies to inform future vaccine
protecting an individual from disease outweigh the risks from potential trials. For example, safety information from preclinical trials of mRNA
side effects (fig. 1). The most common side effects stem from the body’s flu vaccine candidates in 2017 allowed for the acceleration of mRNA
immune reaction and include swelling at the injection site, fever, and aches. COVID-19 vaccine development. Vaccine candidates shown to be safe in
these preclinical trials can proceed to clinical trials in humans.
In the U.S., clinical trials generally proceed through three phases of
testing involving increasing numbers of volunteers: dozens in phase 1 to
thousands in phase 3. Although data may be collected over years, most
common side effects are identified in the first 2 months after vaccination
in clinical trials. After reviewing safety and other data from vaccine
studies, the Food and Drug Administration (FDA) may license a vaccine
to be marketed in the U.S. There are also programs to expedite—but not
bypass—development and review processes, such as a priority review
designation, which shortens FDA’s goal review time from 10 to 6 months.
Safety monitoring continues after licensing. For example, health officials
are required to report certain adverse events—such as heart problems—
following vaccination, in order to help identify potential long-term or rare
side effects that were not seen in clinical trials and may or may not be
associated with the vaccine.
Figure 1. Symptoms of polio and side effects of the polio vaccine. A vaccine is generally
considered safe if its benefits (preventing disease) outweigh its risks (side effects).
In rare cases, some vaccines may cause more severe side effects. For
example, the vaccine for rotavirus—a childhood illness that can cause
severe diarrhea, dehydration, and even death—can cause intestinal
blockage in one in 100,000 recipients. However, the vaccine is still
administered because this very rare side effect is outweighed by the
vaccine’s benefits: it saves lives and prevents an estimated 40,000 to
50,000 childhood hospitalizations in the U.S. each year.
The two messenger RNA (mRNA) vaccines authorized for COVID-
19—a disease that contributed to more than 415,000 American deaths
between January 2020 and January 2021—can cause severe allergic
reactions. However, early safety reporting found that these reactions have
been extremely rare, with only about five cases per 1 million recipients,
according to data from January 2021 reports by the Centers for Disease
Control and Prevention.
Figure 2. Vaccine safety is assessed at every stage: development through post-licensure.
In general, side effects from vaccines are less acceptable to the public
than side effects from treatments given to people who already have a Following a declared emergency, FDA can also issue emergency use
disease. authorizations (EUA) to allow temporary use of unlicensed vaccines
if there is evidence that known and potential benefits of the vaccine
GAO-21-342SP Vaccine Safety
Science, Technology Assessment,
and Analytics
outweigh known and potential risks, among other criteria. As of January /// CHALLENGES
2021, two COVID-19 vaccines had received EUAs, after their efficacy and
short-term safety were assessed through large clinical trials. However, There are a number of challenges to ensuring safe vaccines:
developers must continue safety monitoring and meet other requirements
if they intend to apply for FDA licensure to continue distribution of these ■ Public confidence. Vaccine hesitancy, in part due to misinformation
vaccines after the emergency period has ended. or historic unethical human experimentation, decreases participation
in clinical trials, impeding identification of side effects across
What are the knowledge gaps? One knowledge gap that can remain individuals with different racial, ethnic, and socioeconomic
after clinical trials is whether side effects or other adverse events may backgrounds.
occur in certain groups. For example, because clinical trials usually ■ Mutating viruses. Some viruses, such as those that cause the flu or
exclude certain populations, such as people who are pregnant or have COVID-19, may mutate rapidly and thus may require new or updated
existing medical conditions, data on potential adverse events related to vaccines, for which ongoing safety monitoring is important.
specific populations may not be understood until vaccines are widely
administered. ■ Long-term and rare effects. Exceedingly rare or long-term
effects may not be identified until after vaccines have been widely
In addition, it can be difficult to determine the safety of new vaccines administered. Further study is needed to detect any such effects and
if outbreaks end suddenly. For example, vaccine safety studies were confirm they are truly associated with the vaccine.
hindered during the 2014-2015 Ebola epidemic when a large increase in
the number of cases was followed by a sharp decrease. This disrupted the /// POLICY CONTEXT AND QUESTIONS
clinical trials of Ebola vaccine candidates, because the trials require many
infected and non-infected people. ■ What steps can policymakers take to improve public trust and
understanding of the process of assessing vaccine safety?
Furthermore, a lack of understanding and/or misinformation about the
■ How can policymakers convey the social importance of vaccines to
steps taken to ensure the safety of vaccines hinders accurate public
protect the general public and those who are most vulnerable?
knowledge about safety concerns, which may cause people to delay or
refuse vaccination. This resulting hesitancy may, in turn, increase deaths, ■ How can policymakers leverage available resources to support
social harm, and economic damage. ongoing vaccine development and post-licensure safety monitoring?
/// OPPORTUNITIES /// SELECTED GAO WORK
Continuing and, where necessary, improving existing vaccine safety GAO has previously issued the following related products:
practices offers the following opportunities to society:
■ COVID-19: Federal Efforts Accelerate Vaccine and Therapeutic
■ Herd immunity. Widespread immunity in a population, acquired in Development, but More Transparency Needed on Emergency Use
large part through safe and effective vaccines, can slow the spread Authorizations, GAO-21-207.
of infection and protect those most vulnerable. ■ Operation Warp Speed: Accelerated COVID-19 Vaccine
■ Health care improvements. Vaccinations can reduce the burden on Development Status and Efforts to Address Manufacturing
the health care system by reducing severe symptoms that require Challenges, GAO-21-319.
individuals to seek treatment.
/// SELECTED REFERENCES
■ Eradication. Safe vaccination programs, such as those combatting
smallpox, may eliminate diseases to the point where transmission no Centers for Disease Control and Prevention, Vaccine Safety. Accessed January 12, 2021,
longer occurs. https://www.cdc.gov/vaccinesafety/index.html.
Food and Drug Administration, Vaccine Safety & Availability. Accessed January 12, 2021,
https://www.fda.gov/vaccines-blood-biologics/safety-availability-biologics.
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advances in science and technology. It contains information prepared by GAO
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Timothy M. Persons, PhD, Chief Scientist, personst@gao.gov contain copyrighted images or other material, permission from the copyright holder
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Staff Acknowledgments: Karen Howard (Director), Sarah Harvey (Assistant
Director); Caitlin Dardenne (Analyst-in-Charge); Kristy Hammon; Nacole King;
Anika McMillon; and Ben Shouse.
GAO-21-342SP Vaccine Safety
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