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CDC Study: Pfizer and Moderna Vaccines ‘Highly Effective’ at Preventing COVID Infections

A person walks past the Pfizer headquarters building in New York City, November 9, 2020. (Carlo Allegri/Reuters)

A new CDC study confirms that the Pfizer and Moderna COVID vaccines are highly effective at preventing asymptomatic infections as well as symptomatic infections:

A new CDC study provides strong evidence that mRNA COVID-19 vaccines are highly effective in preventing SARS-CoV-2 infections in real-world conditions among health care personnel, first responders, and other essential workers.  These groups are more likely than the general population to be exposed to the virus because of their occupations.

The study looked at the effectiveness of Pfizer-BioNTech and Moderna mRNA vaccines in preventing SARS-CoV-2 infections among 3,950 study participants in six states over a 13-week period from December 14, 2020 to March 13, 2021.

Results showed that following the second dose of vaccine (the recommended number of doses), risk of infection was reduced by 90 percent two or more weeks after vaccination. Following a single dose of either vaccine, the participants’ risk of infection with SARS-CoV-2 was reduced by 80 percent two or more weeks after vaccination. [emphasis added]

Studies of the Pfizer vaccine in Israel have yielded similar results

For months, some public-health officials in the United States have been underselling the benefits of COVID vaccinations by overstating concerns that vaccinated Americans might be infected without symptoms and easily transmit the SARS-Cov-2 virus to others. As the New York Times noted in January: “Although no rigorous study has yet analyzed whether vaccinated people can spread the virus, it would be surprising if they did. ‘If there is an example of a vaccine in widespread clinical use that has this selective effect — prevents disease but not infection — I can’t think of one!’ Dr. Paul Sax of Harvard has written in The New England Journal of Medicine. (And, no, exclamation points are not common in medical journals.) On Twitter, Dr. Monica Gandhi of the University of California, San Francisco, argued: ‘Please be assured that YOU ARE SAFE after vaccine from what matters — disease and spreading.’”


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