Study Reveals Declining COVID-19 Vaccine Efficacy Against Infection

The vaccines remain protective against serious disease and death.

Written byAnnie Melchor

| 2 min read

Black male doctor wearing a white lab coat and a mask vaccinates Black woman (also wearing a mask) in a medical office.

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Post-COVID-19 vaccine immunity seems to be waning, according to a report published yesterday (August 24) in the US Centers for Disease Control and Prevention’s Morbidity and Mortality Weekly Report.

The study followed more than 4,000 healthcare workers and other frontline essential workers across six states for 35 weeks, testing study participants weekly for SARS-CoV-2 infection, according to STAT. The majority of the participants received one of the three vaccines in use across the US—Pfizer, Moderna, and Johnson & Johnson—although most received the Pfizer vaccine. The study started collecting data on December 14, 2020, and as of early April 2021, it showed that the vaccines were approximately 90 percent effective at preventing symptomatic and asymptomatic SARS-CoV-2 infection.

Today’s report tracked the cohort through August 14—incorporating over four more months of data that include a time period in which the Delta variant swept the country—and found that overall, vaccine ...

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Meet the Author

Annie Melchor
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Stephanie "Annie" Melchor got her PhD from the University of Virginia in 2020, studying how the immune response to the parasite Toxoplasma gondii leads to muscle wasting and tissue scarring in mice. While she is still an ardent immunology fangirl, she left the bench to become a science writer and received her master’s degree in science communication from the University of California, Santa Cruz, in 2021. You can check out more of her work here.
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