Defining COVID-19 Terms: Breakthrough Infection

April 27, 2021


Elizabeth (Izzy) Montgomery, MPA
Policy Analyst

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As vaccination rates continue to rise, there have been reports of individuals becoming infected with COVID-19 despite being fully vaccinated. These cases, known as “breakthrough infections,” have been widely discussed in recent news reports. But why and how often do breakthrough infections occur?

A breakthrough infection (also known as a breakthrough case) is a term used to describe a COVID-19 infection that occurs in a fully vaccinated person. The Centers for Disease Control and Prevention (CDC) defines a person with a breakthrough infection as someone who has a positive COVID-19 test 14 or more days after receiving a full course of a COVID-19 vaccine. State health departments report vaccine breakthrough infections to the CDC.

According to data analyzed by the CDC through April 20, more than 87 million people have been fully vaccinated against COVID-19. Of those individuals, 7,157 are reported to have had breakthrough infections. Sixty-four percent of the breakthrough infections have occurred in females, and 46% have occurred in people age 60 and over. Thirty-one percent of the people who experienced breakthrough infections had no symptoms, 7% were hospitalized (although some of those hospitalizations were reported as not related to COVID-19), and less than 1% have died (although some of those deaths were also reported as not related to COVID-19).

Some breakthrough infections were expected when vaccination efforts were initiated. Although the COVID-19 vaccines are highly effective at preventing symptomatic infection and represent a critical aspect of pandemic control, none of the vaccines is 100% effective at preventing infection. All three of the COVID-19 vaccines currently available in the U.S. (produced by Pfizer, Moderna, and Johnson & Johnson) are highly protective against severe disease and hospitalizations.

Even after becoming fully vaccinated, it is important to continue following CDC guidance for fully vaccinated people. Continuing to wear masks in indoor public settings, avoiding large indoor gatherings, and continuing to practice good hand hygiene are all necessary practices to limit the risk of COVID-19 infection.

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