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VA research shows vaccines more than 95% effective in preventing infection in high-risk population


July 22, 2021

Pittsburgh , PA — Researchers from VA Pittsburgh Healthcare System found that two of the most used coronavirus vaccines, Pfizer and Moderna, are more than 95% effective in preventing confirmed infection.

The study was published in the Annals of Internal Medicine. Variants of the virus, such as the Delta variant, were not specifically addressed, nor was the Johnson & Johnson vaccine.

“Because veterans are at particularly high risk given their older age and greater burden of comorbidities compared with the general population, these findings should be reassuring,” said Dr. Adeel Butt, primary investigator.

Butt and other researchers looked at the health records of more than 54,000 veterans who had coronavirus testing by VA between December 2020 and March 2021 to evaluate the short-term effectiveness of vaccines in preventing infection. Veterans were tested for the virus at least seven days after their second shot.

A large sampling of those who tested positive for infection and those who tested negative in groups that were either vaccinated or unvaccinated showed the Pfizer vaccine was 96.2% effective. The Moderna vaccine was somewhat higher at 98.2%.

The study showed that “vaccine effectiveness was numerically similar (though statistically significantly higher) among persons aged 70 years or older compared with those younger than 70 years…” 

Effectiveness, he said, was also similar between Blacks and whites, men and women, and those with and without more risk factors.

“These findings clearly show the effectiveness of the current vaccines in preventing infection,” Butt said.

The study did not assess vaccine effectiveness in preventing severe disease and death.

Data for the study came from VA’s COVID-19 Shared Data Resource with administrative support from the Veterans Health Foundation.

Media: The corresponding author, Adeel A. Butt, MBBS, MS, can be reached through Sheila Tunney at

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Sheila Tunney, Public Affairs Specialist


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