Study Shows Pfizer and Moderna Vaccines Are Highly Effective, Results Featured at White House Briefing

Woman receiving vaccine shot in arm by healthcare clinician

Allison Naleway, PhDAllison Naleway, PhD

A CDC-funded study conducted at the Kaiser Permanente Center for Health Research and at several other sites across the U.S. found that both the Pfizer and Moderna vaccines are highly effective at preventing infection with SARS-CoV-2, the virus that causes COVID-19. In a White House press briefing on March 29th, CDC Director Rochelle Walensky called the results of the study “tremendously encouraging.”

Among essential workers, who were likely to be exposed to the virus, the study found that the Pfizer and Moderna vaccines were 80% effective at preventing infection at 14 days after the first dose, and 90% effective at 14 days after the second dose. The study’s nearly 4,000 participants were health care workers, first responders such as firefighters, law enforcement, and paramedics, and essential workers, such as teachers, delivery, grocery, and retail workers.

The new findings are consistent with findings from the Phase 3 Clinical Trials that tested these vaccines, but this is the first U.S. study to examine the vaccines’ effectiveness in the real world. According to Allison Naleway, PhD, who led the Kaiser Permanente study site, “We expect that in the real world, effectiveness may be lower than in a clinical trial. It’s very reassuring to see these effectiveness estimates are consistently high in people who were some of the first vaccine recipients outside of the trials.” 

In the new study, called RECOVER-HEROES, researchers collected nasal swabs from participants that were tested weekly for SARS-CoV-2, regardless of symptoms. Since this population was prioritized to receive the vaccine, over the course of the study’s 13 weeks, 2,479 participants (62.8%) received both vaccine doses and 477 (12.1%) received only one dose. Dr. Naleway’s Portland-area study site contributed 468 participants to the study’s total population of 3,950. Participants also joined the study in Florida, Minnesota, Texas, Utah, and Arizona.

The RECOVER-HEROES study is still recruiting participants. If you believe you fit the eligibility criteria, are unvaccinated, and would like to join, visit the study website or call 1-888-687-7087.

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