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Pfizer vaccine protection wanes after 6 months, study finds


Pfizer’s COVID-19 vaccine continues to show strong protection against serious illness and hospitalization after 6 months, but overall protection against the virus appears to wane after a half a year, according to a new study.

The July 28 preprint report of the study, which has not been peer reviewed, suggests a gradual “declining trend in vaccine efficacy” over 6 months after two doses of the Pfizer vaccine in more than 45,000 people worldwide.

The study finds overall effectiveness falls from 96% to 84%.

At the same time, a third booster dose of the Pfizer vaccine increases neutralizing antibody levels against the Delta variant by more than five times, compared to levels after just a second dose in people aged 18-55 years, new data from Pfizer shows.

The third-dose immune response appears even more robust – more than 11 times higher than the second shot – among people aged 65-85 years.

The company noted this could mean an estimated 100-fold increase in Delta variant protection after a third dose. These new findings are outlined in a Pfizer second-quarter 2021 earnings report, which notes that the data are submitted for publication in a medical journal.

The data come from a relatively small number of people studied. There were 11 people in the 18- to 55-year-old group and 12 people in the 65- to 85-year-old group.

“These preliminary data are very encouraging as Delta continues to spread,” Mikael Dolsten, MD, chief scientific officer and president of the Worldwide Research, Development, and Medical organization at Pfizer, said during prepared remarks on a company earnings call July 28, CNN reported.

Availability of a third dose of any of the current COVID-19 vaccines would require amendment of the Food and Drug Administration’s emergency use authorization, or full FDA approval for the vaccine.

The possibility of a third dose authorization or approval has not been without controversy. For example, when Pfizer announced intentions to file for FDA authorization of a booster dose on July 8, the Centers for Disease Control and Prevention, the FDA, and the National Institutes of Health were quick to issue a joint statement saying they would decide when the timing is right for Americans to have a third immunization. The agencies stated, in part, “We are prepared for booster doses if and when the science demonstrates that they are needed.”

In addition, the World Health Organization said at a media briefing on July 12 that rich countries should prioritize sharing of COVID-19 vaccine supplies to other countries in need worldwide before allocating doses for a booster shot for its own residents.

A version of this article first appeared on

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