Pfizer/BioNTech COVID-19 Vaccine Efficacy Wanes, Study Says

October 7, 2021

Although efficacy of the Pfizer vaccine against nonDelta COVID-19 infection dropped from 97 percent to 67 percent after five months, its protection against COVID-19 hospital admission — including admissions with Delta variant illness — remained high, according to a large database study published this week in The Lancet.

The review of 3.4 million patient records also found that efficacy against Delta variant infection started out at 93 percent and waned to 53 percent after four months, reported Sara Y. Tartof and colleagues. But the vaccine continued to provide 93 percent protection against Delta-associated hospitalization.

The findings suggest that Delta isn’t driving the vaccine efficacy changes. “Reductions in vaccine effectiveness over time are likely to be primarily due to waning vaccine effectiveness rather than the Delta variant escaping vaccine protection,” wrote Tartof, an infectious disease epidemiologist for Kaiser, and her team.

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