Among 101 million fully vaccinated individuals, a total of 10,262 SARS-CoV-2 vaccine breakthrough infections have been reported in 46 US states and territories as of April 30, 2021, according to a recent Morbidity and Mortality Weekly Report (MMWR) published by the Centers for Disease Control and Prevention (CDC).

For this report, vaccine breakthrough infection was defined as the detection of SARS-CoV-2 RNA or antigen in a respiratory specimen collected from an individual at least 14 days after receiving all recommended doses of an FDA-authorized COVID-19 vaccine. Among the 10,262 reported infections, over 60% occurred in females (n=6446) and the median patient age was 58 years (interquartile range, 40-74 years). Findings showed that 27% (n=2725) of the breakthrough infections were asymptomatic.

Among hospitalized patients (n=995), 29% (n=289) were asymptomatic or hospitalized for a reason unrelated to COVID-19. The median age of patients who died was 82 years (interquartile range, 71-89 years) and 28 (18%) of the 160 deaths were reported to be asymptomatic or unrelated to COVID-19.

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A total of 555 (5%) cases had sequence data available, of which 356 (64%) were identified as SARS-CoV-2 variants of concern. These included B.1.1.7 (n=199; 56%), B.1.429 (n=88; 25%), B.1.427 (n=28; 8%), P.1 (n=28; 8%), and B.1.351 (n=13; 4%).

“Even though FDA-authorized vaccines are highly effective, breakthrough cases are expected, especially before population immunity reaches sufficient levels to further decrease transmission,” the CDC’s COVID-19 Vaccine Breakthrough Case Investigations Team noted in their report. “The number of COVID-19 cases, hospitalizations, and deaths that will be prevented among vaccinated persons will far exceed the number of vaccine breakthrough cases.”

In an effort to focus on cases with the highest clinical and public health significance, the CDC has transitioned to investigating only vaccine breakthrough cases that lead to hospitalization or death.


Birhane M, Bressler S, Chang G, et al. COVID-19 Vaccine breakthrough infections reported to CDC — United States, January 1–April 30, 2021. [published online May, 25, 2021]. MMWR Morb Mortal Wkly Rep. doi:

This article originally appeared on MPR