While breakthrough infections still account for a small proportion of COVID-19 cases in the U.S., early evidence suggests their prevalence may be increasing as Americans' immunity wanes and the delta variant continues to spread, The New York Times reported Aug. 17.
The Times' examined preliminary data from seven states keeping detailed data on breakthrough cases: California, Colorado, Massachusetts, Oregon, Utah, Vermont and Virginia.
In six of these states, breakthrough cases accounted for 18 percent to 28 percent of new COVID-19 infections in recent weeks, according to the Times. States also reported higher percentages of hospitalization and deaths among unvaccinated Americans than previously seen. The Times said these trends may not apply to other states, and that scientists typically expect breakthrough cases to increase as more people are vaccinated.
Overall, breakthrough infections made up a tiny portion of a state's total infections, suggesting that the vaccine is still highly protective, according to the Times. For example, in California, breakthrough cases that led to hospitalization represented .007 percent of the nearly 22 million fully vaccinated residents in the state.
But emerging research from the United States, Israel, Britain and Qatar suggests the vaccine's efficacy may be decreasing, according to The Washington Post. In August, CDC Director Rochelle Walensky, MD, told reporters that data supporting her earlier comments that 97 percent of COVID-19 hospitalizations involve unvaccinated people was out of date, according to the Post. The agency has not released a new estimate.
HHS shared a formal plan for administering booster shots Aug. 18, which the agency said was based on data that made it "very clear" COVID-19 vaccines' protection wanes over time.