SARS-CoV-2 mRNA Vaccine Effectiveness in the Borriana COVID-19 Cohort: A Prospective Population-Based Cohort Study

Background and Objective: Evaluating vaccine effectiveness (VE) is essential to implementing prevention strategies, and our objective was to estimate the VE of SARS-CoV-2 messenger RNA (mRNA) vaccines in preventing SARS-CoV-2 infection. Materials and Methods: We carried out a population-based, prospective cohort study on the Borriana COVID-19 cohort (Valencia Community, Spain) during the 2021–2023 period, considering all SARS-CoV-2 cases that occurred after the SARS-CoV-2 vaccine campaign started in January 2021 (first approach), as well as only symptomatic cases (second approach). Multivariable robust Poisson regression models were employed. Results: In this cohort with 301 participants, 285 were vaccinated, among whom 228 received only SARS-CoV-2 mRNA vaccines, and 57 received mRNA vaccines and other vaccines. In the first approach, there were 226 cases and 75 non-cases. The adjusted VE for three doses of vaccine was 37% (95% confidence interval [CI]: 22–49%) to prevent infection. In the second approach, with 153 symptomatic cases after excluding 73 asymptomatic cases, the adjusted VE for three doses of vaccine was 50% (95% CI 33–63%) to prevent symptomatic infection. Three doses of vaccine exhibited modest but significant protection against infection and symptomatic infection. Conclusions: This study recommends surveilling SARS-CoV-2 infections and variants, vaccinating at-risk populations, and developing new vaccines.