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COVID-19: Vaccine Safety and Effectiveness

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COVID-19 vaccines are safe and effective. Hundreds of millions of people have received COVID-19 vaccines under the most intense safety monitoring in U.S. history.

It is recommended that everyone 6 months and older get vaccinated as soon as possible.

Information on available vaccines

There are three COVID-19 vaccine brands available in the United States: Pfizer-BioNTech, Moderna, and Novavax.

Here’s what’s important to know:

  • Everyone 6 months and older in the United States is recommended to get a 2023–2024 updated COVID-19 vaccine for the best protection against serious illness from COVID-19.
  • All COVID-19 vaccines are effective in preventing serious outcomes of COVID-19, including severe disease, hospitalization, and death.
  • Adverse events after getting vaccinated are extremely rare and the benefits of vaccination outweigh the risks.
  • Some people may have side effects that go away within a few days after getting their COVID-19 vaccine. Learn more about common side effects.

Vaccine effectiveness

Vaccine effectiveness is a measure of how well vaccination protects people against outcomes such as infection, symptomatic illness, hospitalization, and death. Vaccine effectiveness is measured through observational studies.

Clinical trials and vaccine effectiveness studies show that being up to date with COVID-19 vaccines provides strong protection against severe disease, hospitalization, and death in all age groups. All eligible people should remain up to date on their COVID-19 vaccines for the best protection. Learn more and see vaccine effectiveness data by visiting: CDC (Centers for Disease Control and Prevention) COVID Data Tracker: Vaccine Effectiveness.

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FDA clinical trials

Before the U.S. Food and Drug Administration (FDA) can approve a vaccine, it must be tested through clinical trials to make sure it is safe and to see how well it prevents illness. COVID-19 vaccines were, and continue to be, tested in large clinical trials, made up of far more participants than is usually required, to make sure they met well-established safety standards. Vaccines are also continually assessed and evaluated for safety with new populations, such as children. The participants of the trials include people of different ages, races, and ethnicities, as well as those with different medical conditions to make sure each vaccine is effective. Learn more about how medical experts ensure vaccines work both in clinical trials and the real world through this overview of the COVID-19 vaccine clinical trial and approval process or the FDA webpage on Vaccine Development 101.

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Continuous safety monitoring

The following systems continue to track common side effects and rare adverse, sometimes serious, reactions in people who receive any vaccine, including COVID-19 vaccines. The CDC and FDA monitor these systems in real time to make sure safety issues are detected as quickly as possible.

  • The Vaccine Adverse Event Reporting System (VAERS) is the national system that collects reports from health care professionals, vaccine manufacturers, and the public on adverse events that happen after vaccination. Reports of adverse events that are unexpected, appear to happen more often than expected, or have unusual patterns are followed up with specific studies. Providers are required to report any adverse events to this system. VAERS has alerted public health experts and the public about the very rare adverse events following COVID-19 vaccination: Thrombosis with thrombocytopenia syndrome (TTS), Guillain-Barré Syndrome (GBS), myocarditis, and pericarditis.
  • Vaccine Safety Data Link is a network of nine integrated health care organizations across the U.S. that conduct active surveillance and research. The system is also used to help determine whether possible side effects identified through VAERS are actually related to vaccination.
Last revised March 13, 2024