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Clinical trials have reported efficacies >94% for mRNA SARS-CoV-2 vaccines in preventing symptomatic disease, with lower efficacy against infection. As population-based data are important for formulating policies, investigators used U.S. Veterans Affairs data to study the short-term effectiveness of the Pfizer-BioNTech and Moderna vaccines in preventing confirmed infection. A total of 54,360 veterans (83.6% male; median age, 61; 19.9% Black; median body-mass index, 31 kg/m2) tested positive for SARS-CoV-2 between Dec 15, 2020, and March 4, 2021. For each subject who tested positive, a propensity score–matched control who tested negative was identified.
Among participants testing positive, 9800 (18%) had been vaccinated. Overall vaccine effectiveness ≥7 days after the second dose was 97.1%. By vaccine type, effectiveness was 96.2% (Pfizer-BioNTech) and 98.2% (Moderna). Effectiveness was similar regardless of age, race/ethnicity, gender, or comorbidities.
Butt AA et al. SARS-CoV-2 vaccine effectiveness in a high-risk national population in a real-world setting. Ann Intern Med 2021 Jul 20; [e-pub]. (https://doi.org/10.7326/M21-1577)
Comment
This large population-based study confirms just how effective the SARS-CoV-2 mRNA vaccines can be for preventing SARS-CoV-2 infection. The investigators did not assess effectiveness for preventing severe disease or death; moreover, because the study was conducted “pre-Delta,” the findings are not necessarily applicable now that Delta is the predominant variant in circulation.