HealthDay News — Authorized mRNA vaccines are effective for preventing SARS-CoV-2 infection, and attenuate viral load, risk of febrile symptoms, and duration of illness in cases of breakthrough infection, according to a study published online June 30 in the New England Journal of Medicine.

Mark G. Thompson, PhD, from the US Centers for Disease Control and Prevention in Atlanta, and colleagues conducted a prospective cohort study involving 3975 health care personnel, first responders, and other essential and frontline workers to examine the effectiveness of 2-dose mRNA vaccines in preventing SARS-CoV-2 infection in real-world conditions. Participants completed weekly SARS-CoV-2 testing from December 14, 2020, to April 10, 2021.

The researchers found that SARS-CoV-2 was detected in 204 participants: 5, 11, and 156 of whom were fully vaccinated (14 or more days after dose 2), partially vaccinated (14 or more days after dose one and 14 or less days after dose 2), and unvaccinated, respectively; 32 participants had indeterminate vaccine status (less than 14 days after dose 1) and were excluded. The adjusted vaccine effectiveness was 91 and 81 percent, respectively, with full and partial vaccination. Among those with SARS-CoV-2 infection, compared with unvaccinated participants, partially or fully vaccinated participants had a 40% lower mean viral RNA load. In addition, they had a lower risk of febrile symptoms (relative risk, 0.42) and shorter duration of illness (2.3 fewer days spent sick in bed).

“Authorized mRNA vaccines were highly effective among working-age adults in preventing SARS-CoV-2 infection when administered in real-world conditions,” the authors write.

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