Factors Associated with Post-vaccination Immunity Against COVID-19 in Benin

Introduction: Vaccination remains the primary strategy against COVID-19. However, data may not reflect actual population immunity. This study aims to determine the seroprevalence of post-vaccination immunity against COVID-19 in Benin and identify associated factors. Methods: A cross- sectional descriptive and analytical study was conducted from April to September 2023 in 21 hospital centers across Benin's twelve departments and included 3802. Post-vaccination immunity was defined by the presence of anti-SARS-CoV-2 Spike IgG antibodies and the absence of anti-NCP IgG antibodies, using the Euroimmun ELISA test. Data were analyzed using STATA software with multivariate logistics regression. Results: Seroprevalence of post-vaccination immunity was 41.56%. In multivariate analysis, factors associated with this immunity were age (adjusted OR=1.56; 95% CI [1.09-2.59]), residence within the former sanitary cordon (aOR=1.34; 95% CI [1.14-3.01]), history of hypertension/cardiovascular disease (aOR=3.25; 95% CI [1.41-4.63]), and history of diabetes (aOR=2.73; 95% CI [1.89-3.93]). Conclusion: Post-vaccination immunity is higher among vulnerable groups (elderly, comorbidities) and those in strategic urban zones, reflecting the prioritization of vaccination campaigns. Recommendations are proposed to target younger populations and rural areas to strengthen collective immunity.