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A Project of The Annenberg Public Policy Center
SciCheck’s COVID-19/Vaccination Project

How effective are the vaccines?


This article is available in both English and Español

All of the authorized and approved vaccines are effective at preventing symptomatic disease.

The Pfizer/BioNTech vaccine, which is the first COVID-19 vaccine to receive full approval from the Food and Drug Administration, showed a final efficacy of 91% against symptomatic illness in its phase 3 trial, meaning that under the conditions of the trial the vaccine reduced the risk of getting sick by 91%. The Moderna vaccine showed similar results in its clinical trial, with an efficacy of 94% against disease at the time of emergency use authorization.

Johnson & Johnson, which partly tested its vaccine in South Africa when the beta variant emerged, reported an efficacy of 66% in preventing moderate to severe COVID-19 and an efficacy of 85% in preventing severe or critical COVID-19.

Subsequent studies have demonstrated that the vaccines are effective under real-world conditions, including against the highly contagious delta variant, although they are less effective in preventing infection and mild disease compared with earlier versions of the virus. Most studies show the vaccines remain highly effective in preventing serious disease, hospitalization and death from delta.

Data also suggest that vaccinated people are less likely to transmit the coronavirus if they do become infected.