Breakthrough infections post-vaccination are expected, but uncommon

News of “breakthrough” infections occurring in fully vaccinated people might seem concerning, but some breakthrough cases are expected. The vaccines remain extremely effective. 

A so-called breakthrough infection is an infection that occurs at least two weeks after complete vaccination (two doses of an mRNA vaccine or one dose of the Johnson & Johnson vaccine). No vaccine has ever, for any disease, been 100% effective. But  real-world data has shown that the Moderna and Pfizer vaccines prevent more than 90% of infections, and Johnson & Johnson’s vaccine prevents more than 66% of infections. They are tremendously effective.

But here’s the most important point: all of the COVID vaccines almost completely prevent severe disease, hospitalization, and death. As of August 16th, the CDC reported that more than 168 million Americans have been vaccinated, and only 9,716 reported breakthrough infections have led to patients’ hospitalization or death. This data is likely an undercount because reporting is voluntary, but even accounting for that, vaccination is extremely effective against severe outcomes.

More contagious COVID variants might increase the breakthrough infection rate. But getting more people vaccinated is the best way to stop new variants before they start. New variants like Delta are more likely to develop as the disease spreads to more people. Since the vaccines are extremely effective at slowing COVID’s spread, they’re our strongest defense against its current variants, and against the development of new ones.

Last update: Sept 10, 2021, 8:00pm ET

Science review: ERS, AGB, GSN