Hundreds of millions of people in the United States have safely received COVID-19 vaccinations. These vaccines have undergone the most intensive safety monitoring in U.S. history that includes both established and new safety monitoring systems.
Results from monitoring show that while some people don’t have side effects after getting a COVID-19 vaccine, many people have mild side effects, like pain or swelling at the injection site, headache, chills, or fever. These reactions are normal signs that your body is building protection. COVID-19 vaccines are effective at protecting you from getting sick. CDC recommends everyone ages 5 years and older get a COVID-19 vaccination as soon as possible.
The U.S. Food and Drug Administration (FDA) has fully approved the use of the Pfizer-BioNTech COVID-19 vaccine in people ages 16 years and older and has authorized its emergency use for children ages 5 years and older. The FDA has fully approved the use of Moderna COVID-19 vaccine in people 18 years and older. The FDA has granted Emergency Use Authorizations (EUA)external icon for Johnson & Johnson’s Janssen COVID-19 vaccine for people ages 18 years and older.
The Pfizer-BioNTech, Moderna, and J&J/Janssen vaccines were shown to be safe and effective in clinical trials. The trials showed that the known and potential risks and benefits of COVID-19 vaccines outweigh the known and potential risks of becoming infected with COVID-19. Learn more in this video about EUAs.
All COVID-19 vaccines currently authorized or recommended for use in the United States are safe and effective. However, CDC recommends that people who are starting their vaccine series or getting a booster dose get either Pfizer-BioNTech or Moderna (mRNA COVID-19 vaccines). The mRNA vaccines are preferred over Johnson & Johnson’s Janssen COVID-19 vaccine in most circumstances. Although mRNA vaccines are preferred, the J&J/Janssen COVID-19 vaccine may be considered in some situations.
Before the U.S. Food and Drug Administration (FDA) approves a vaccine or authorizes a vaccine for emergency use, clinical trials are conducted to determine vaccine effectiveness.
After FDA approves a vaccine or authorizes a vaccine for emergency use, CDC and other federal partners continue to assess the vaccine to determine how well it works under real-world conditions.
Such evaluations will help us understand if vaccines are performing as expected outside the more controlled setting of a clinical trial. As vaccine uptake increases nationally, we also try to understand how well the vaccines:
Several factors can affect real-world vaccine effectiveness, including:
CDC uses several methods to study all of these factors, as they can all contribute different information about how a vaccine is working.
After a vaccine is authorized or approved for use, vaccine safety surveillance systems monitor adverse events and watch for potential safety problems. This continued monitoring can identify adverse events that may not have been seen in clinical trials. If an unexpected adverse event is seen, experts quickly study it further to assess whether it is a true safety concern. Experts then decide whether changes are needed in U.S. vaccine recommendations or clinical guidance. This monitoring is critical to help ensure that the benefits continue to outweigh the risks for people who receive vaccines.
FDA’s COVID-19 Vaccines websiteexternal icon also includes important recommendations for ongoing safety evaluation after any COVID-19 vaccine is made available under EUA.
CDC has expanded safety surveillance through new systems and additional information sources, as well as by scaling up existing safety monitoring systems.
The following systems and information sources add an additional layer of safety monitoring, giving CDC and FDA the ability to evaluate COVID-19 vaccine safety in real time and make sure COVID-19 vaccines are as safe as possible:
As people get vaccinated, CDC, FDA, and other federal partners will use the following existing, robust systems and data sources to conduct ongoing safety monitoring:
Indian Health Service (IHS) Vaccine Safety Monitoring Systems
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