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

Evaluation of vaccine effectiveness (VE) was essential to implement strategies of prevention, and our objective was estimated the VE of SARS-CoV-2 messenger RNA (mRNA) vaccines to prevent SARS-CoV-2 infection. We performed a population-based prospective cohort study in the Borriana COVID-19 cohort (Valencia Community, Spain) during the period 2021-2023, with two approaches, considering firstly, all cases occurred after SARS-CoV-2 vaccine campaign started in January 2021, and then secondly, only symptomatic cases. Multivariable robust Poisson regression models were employed. Results: In first approach, of 301 participants, 285 were vaccinated, 228 with only SARS-CoV-2 mRNA vaccines, and 57 with mRNA vaccine and other vaccines. A total of 226 cases occurred with 75 non-cases. Adjusted VE for 3 doses of vaccine received was 37% (95% Confidence interval [CI] 22%-49%). The second approach, with 153 symptomatic cases, excluding 73 asymptomatic cases, adjusted VE for 3 doses of vaccine received was 50% (95% CI 33%-63%). While one or two doses of vaccines presented a low VE with insufficient to protect against infection, 3 doses of vaccine reached modest and significant protection. Exclusion of asymptomatic cases improved the VE estimation. Conclusion: Development of new vaccines is needed to improve control and prevention strategies against SARS-CoV-2.