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US Study Confirms mRNA Vaccine Effectiveness Against SARS-CoV-2

Last Updated: March 30, 2021.

TUESDAY, March 30, 2021 (HealthDay News) -- Messenger RNA (mRNA) COVID-19 vaccines are effective for preventing severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, with 90 percent effectiveness for full immunization, according to research published in the March 29 early-release issue of the U.S. Centers for Disease Control and Prevention Morbidity and Mortality Weekly Report.

Mark G. Thompson, Ph.D., from the CDC COVID-19 Response Team, and colleagues routinely tested for SARS-CoV-2 infections every week during Dec. 14, 2020, to March 13, 2021, in prospective cohorts of health care personnel, first responders, and other essential and frontline workers in eight locations in the United States. Tests were conducted regardless of symptom status and onset of symptoms consistent with COVID-19.

Among 3,950 participants with no laboratory documentation of SARS-CoV-2 infection, 62.8 and 12.1 percent received both doses and only one dose of mRNA vaccine, respectively. The researchers found that among unvaccinated participants, 1.38 SARS-CoV-2 infections were confirmed per 1,000 person-days. In contrast, 0.04 and 0.19 infections were reported per 1,000 person-days among fully immunized participants (≥14 days after the second dose) and among partially immunized persons (≥14 days after the first dose), respectively. After adjustment for study site, the estimated mRNA vaccine effectiveness was 90 and 80 percent for full and partial immunization, respectively.

"This study shows that our national vaccination efforts are working," CDC Director Rochelle P. Walensky, M.D., M.P.H., said in a statement. "The authorized mRNA COVID-19 vaccines provided early, substantial real-world protection against infection for our nation's health care personnel, first responders, and other frontline essential workers."

One author disclosed financial ties to Pfizer.

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