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The FDA requires that vaccines undergo a rigorous scientific process, including three phases of clinical trials, before they authorize or approve the vaccine. The COVID-19 vaccines are subject to the same safety standards as other vaccine trials. To date, the independent Data and Safety Monitoring Board overseeing Phase 3 trials of the Pfizer and Moderna vaccines has not identified or reported any serious safety concerns. All phase 3 studies have Data Safety and Monitoring Boards. The boards are made up of independent scientists hired by the company to look at the safety data and check at regular intervals whether the company should cancel or continue with the study. Additionally, two independent advisory committees will review a vaccine’s safety data before it is made available to the public. These committees are the Vaccines and Related Biological Products Advisory Committee (VRBPAC), which advises the FDA, and the Advisory Committee on Immunization Practices (ACIP), which advises the CDC. Learn more about the vaccine safety and development process.
The most commonly reported side effects for the COVID-19 vaccines are mild fever, chills, body aches, pain and redness at the injection site, nausea, headache, and fatigue for 1-2 days after receiving the vaccine. Side effects may differ among COVID-19 vaccines. For in-depth information about the side effects of the vaccines, see the CDC’s report on the Pfizer vaccine and the Moderna vaccine.
The process of building immunity can cause symptoms. These symptoms are normal and show that your body’s immune system is responding to a vaccine. Other routine vaccines, like the flu vaccine, have similar side effects. Clinical trial participants for COVID-19 vaccine reported that the discomfort from side effects went away after a day, sometimes sooner. The discomfort can be more pronounced after the second dose of the vaccine. If you experience discomfort after the first dose of the vaccine, it is very important that you still receive the second dose a few weeks later for full protection.
About Serious Side Effects, including Possible Effects on Fertility
Decades of vaccine research demonstrates that most serious side effects generally occur within six weeks of administering a vaccine. For the COVID-19 vaccines, the FDA has required clinical trials to provide data from eight weeks of safety monitoring following the second dose before considering the authorization of a vaccine for public use. Because this is a new vaccine, researchers will be learning more about rare side effects, if any, over the next year. To identify side effects that happen only very rarely (e.g., once in 50,000 doses), hundreds of thousands of people need to be vaccinated and followed over time.
The FDA and CDC will continue to closely monitor vaccine safety as the public begins using a new vaccine. Both agencies have both longstanding and new safety systems in place for heightened monitoring of all COVID-19 vaccines. Learn more about the vaccine safety monitoring systems.
A COVID-19 vaccine will give you protection against the disease without having to get sick with the actual virus. It is not possible to get COVID-19 from a vaccine, but it is possible to get symptoms that are consistent with COVID-19. The vaccine candidates use inactivated virus, parts of the virus (e.g., the spike protein), or a gene from the virus. None of these can cause COVID-19. The goal of the vaccine is to provide your body with the tools it needs to fight the COVID-19 virus if you were to get infected.
Vaccines must go through a detailed scientific evaluation before they can be submitted to the FDA for approval. Each phase of the evaluation includes three different clinical research studies. In the clinical research study or trial, people volunteer to be part of the study. Each clinical trial emphasizes safety of the vaccine on people. As the research moves through to the next phase, the group of volunteers becomes bigger to include more diversity in people and circumstances.
For each vaccine authorized by the FDA, the Advisory Committee on Immunization Practices (ACIP) carefully reviews all available data about the vaccine from clinical trials and other studies, and makes recommendations for vaccine use in the general public. Recommendations include groups that should and should not receive the vaccine, as well as the timing, volume, number, and spacing of doses in a vaccine series.