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

Mark G. Thompson, PhD, from the CDC COVID-19 Response Team, and colleagues routinely tested for SARS-CoV-2 infections every week during December 14, 2020, to March 13, 2021, in prospective cohorts of health care personnel, first responders, and other essential and frontline workers in 8 locations in the United States. Tests were conducted regardless of symptom status and onset of symptoms consistent with COVID-19.

Among 3950 participants with no laboratory documentation of SARS-CoV-2 infection, 62.8% and 12.1% received both doses and only 1 dose of mRNA vaccine, respectively. The researchers found that among unvaccinated participants, 1.38 SARS-CoV-2 infections were confirmed per 1000 person-days. In contrast, 0.04 and 0.19 infections were reported per 1000 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% for full and partial immunization, respectively.

“This study shows that our national vaccination efforts are working,” CDC Director Rochelle P. Walensky, MD, MPH, 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.”


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One author disclosed financial ties to Pfizer.

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