Estimating the number of symptomatic SARS-CoV-2 infections among vaccinated individuals in the United States-January-April, 2021

As of March 2021, three COVID-19 vaccines have been authorized by the U.S. Food and Drug Administration (FDA) for use in the United States. Each has substantial efficacy in preventing COVID-19. However, as efficacy from trials was 77 million fully vaccinated people, reflecting <0.5% of COVID-19 cases that occurred during that time. With ongoing SARS-CoV-2 transmission and increasing numbers of people vaccinated in the United States, vaccine breakthrough infections will continue to accumulate before population immunity is sufficient to interrupt transmission. Understanding expectations regarding number of vaccine breakthrough infections enables accurate public health messaging to help ensure that the occurrence of such cases does not negatively affect vaccine perceptions, confidence, and uptake.