CDC says study of 1,800 U.S. health care workers confirms efficacy of Pfizer and Moderna vaccines

A study released by the Centers for Disease Control and Prevention (CDC) found that the Pfizer-BioNTech and Moderna vaccines were 94 percent effective in preventing symptomatic COVID-19 among 1,843 health care workers in 25 states, providing "the most compelling information to date that COVID-19 vaccines were performing as expected in the real world," CDC Director Dr. Rochelle Walensky said in a statement Friday. "This study, added to the many studies that preceded it, was pivotal to CDC changing its recommendations for those who are fully vaccinated."

More than 80 percent of the study participants were female, the median age of all participants was 37 to 38, and all of them were tested regularly. The 94 percent effectiveness rate was in line with the Pfizer and Moderna clinical trials, but the study also found that one dose of the vaccine was 82 percent effective, higher than in previous studies, possibly because of the relative youth of the participants.

Both vaccines are very effective against the B.1.1.7 coronavirus variant first discovered in Britain and now the dominant strain in the U.S. For several reasons, the vaccines being among the most significant, a surge of variant-driven infections experts were bracing for in December "ended up a mere blip in most of the country," The New York Times reports. "The nationwide total of daily new cases began falling in April and has now dropped more than 85 percent from the horrific highs of January."

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