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

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.

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.

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.

This study recommends surveilling SARS-CoV-2 infections and variants, vaccinating at-risk populations, and developing new vaccines.