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How will we know that the vaccine is safe and protects people from COVID-19?

Tens of thousands of people volunteered for what are called clinical trials to find out whether a vaccine is safe and effective at protecting people from COVID-19. These trials include people of racially and ethnically diverse backgrounds. The results of the trials are reviewed by independent experts, companies that are making the vaccine, and a federal government agency called the Food and Drug Administration (FDA).

Trials for the COVID-19 vaccine began earlier this year, and the Pfizer-BioNTech and Moderna vaccines that have received Emergency Use Authorizations from the Food and Drug Administration were found to be 95 and 94 percent effective, respectively, which is terrific. Vaccine safety gets assessed based on the experience of volunteers who received the vaccine during the trials. Thousands of volunteers are followed closely for at least two months to monitor their health before the vaccine can be authorized for use. Any negative reactions to a vaccine would most likely happen within that period. The volunteers are also observed long-term to monitor for any other problems.

In February 2021, the Centers for Disease Control and Prevention (CDC) released a report analyzing safety data for the first month of vaccination with the Pfizer-BioNTech and Moderna vaccines. Overall, the CDC researchers had confidence in the safety of both vaccines. 13.8 million doses were administered with only about 7000 adverse effects reported. Over 90% of reported adverse effects were nonserious and included symptoms like fatigue, headache, and dizziness. You can report any side effects following your COVID-19 vaccination to the CDC via the Vaccine Adverse Event Reporting System or the V-safe mobile app.

Pfizer, in partnership with the Israel Ministry of Health, announced that its vaccine was 94% effective at preventing asymptomatic disease. This study was done with the B.1.1.7 variant, first discovered in the U.K., as the dominant variant.

Updated 12 March 2021

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