Per the CDC, a booster dose of COVID-19 vaccine is recommended for all persons aged 18 or older, at least 6 months after completion of a mRNA vaccine (Pfizer-BioNTech or Moderna) primary series, or at least 2 months after receipt of the single primary dose Janssen vaccine. Teens age 16-17 who received Pfizer's vaccine can get a booster (Pfizer is the only booster currently authorized for persons under 18). See the table for other recommendations.

When available, the 95% Confidence Intervals are provided [in square brackets] for estimated vaccine efficacies. This is the range of values that we can be 95% confident contains the true efficacy for a study population. The narrower the range or Interval, the more precise the estimate of efficacy. In general, studies with larger sample sizes will have narrower confidence intervals. Confidence intervals where the lower estimate of efficacy is negative are so imprecise that one has little confidence of the efficacy estimate.

Our methods

These vaccines were chosen because their trial results have been published in detail and they have been authorized for use in the United States or in other countries.

Sources of general information about the vaccines, such as their technology, storage conditions, and number of administered doses, are the New York Times Vaccine Tracker and the Centers for Disease Control and Prevention (CDC).

Sources of information about the efficacy and safety of the vaccines are the published clinical trials themselves, U.S. Food and Drug Administration (FDA) documents, and a company announcement from AstraZeneca about the results of its latest trial in the United States. Efficacy data based on completion of recommended number of vaccine injections.

Sources of information about planned or in-progress vaccine trials are clinicaltrials.gov, company announcements, and news reports such as The Medical Letter.

This website is updated as new published data become available.