In a publication in the Annals of Internal Medicine, researchers conducted a test-negative, case-control study using condition logistic regression. The objective of the study was to assess the short-term effectiveness of the vaccines in preventing COVID-19 infection. The study was conducted in the U.S. Department of Veterans Affairs health system, and the participants were comprised of veterans who had been tested for SARS-CoV-2 infection between December 15, 2020, and March 4, 2021, and who had no confirmed infection before December 15, 2020. The study intervention was vaccination with either the BNT-162b2 (Pfizer–BioNTech) or mRNA-1273 (Moderna) vaccine as part of routine clinical care.

The researchers found that among 54,360 individuals who tested positive and 54,360 propensity score–matched control participants, the average age was 61 years, 83.6% were male, and 62% were Caucasian. Average body mass index was 31 kg/m2 among those who tested positive and 30 kg/m2 among those who tested negative. Among those who tested positive, 9,800 (18.0%) had been vaccinated; among those who tested negative,17,825 (32.8%) had been vaccinated. Overall vaccine effectiveness 7 or more days after the second dose was 97.1% (95% confidence interval [CI], 96.6%-97.5%). Effectiveness was 96.2% (CI, 95.5%-96.9%) for the Pfizer–BioNTech BNT-162b2 vaccine and 98.2% (CI, 97.5%-98.6%) for the Moderna mRNA-1273 vaccine. Effectiveness remained above 95% regardless of age group, gender, race, or presence of comorbidities.

The authors indicated that the currently used SARS-CoV-2 vaccines are more than 95% effective in preventing confirmed infection. They also noted that veterans are at particularly high risk given their older age and greater burden of comorbidities compared with the general population, and the high level of vaccine effectiveness witnessed is encouraging. They also remarked that their results are comparable to those of a recent study in Israel, which found effectiveness of 92% for infection prevention with the Pfizer–BioNTech BNT-162b2 vaccine.

Although these two studies had different designs and evaluated different populations, the remarkably comparable results provide further reassurance of the effectiveness of the vaccines in preventing infection in various real-world settings. The authors noted that limitations of their study were the following: predominantly male population; lack of data on disease severity, mortality, and effectiveness by SARS-CoV-2 variants of concern; and short-term follow-up.

The authors concluded that the currently available mRNA vaccines are highly effective in preventing confirmed infection in a high-risk population in a real-world setting. Finally, the authors noted that further studies are needed to ascertain vaccine effectiveness in other populations (such as women and younger individuals) and the effect of vaccination on other serious outcomes.

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