Seroprevalence and persistence of humoral immunity in response to SARS-CoV-2 vaccination and mild infection in Morocco: a cross-sectional study.

INTRODUCTION

assessing the seroprevalence and persistence of humoral immunity through population-based serological surveys is crucial for predicting reinfection risk and optimizing vaccination strategies. In Morocco, a mass vaccination campaign against SARS-CoV-2 has been launched to achieve herd immunity and reduce virus transmission. This study evaluated the humoral immune response to the BBIBP-CorV and ChAdOx1 nCoV-19 vaccines in healthy donors with varying doses and infection histories.

METHODS

IgG levels were measured via Vircell COVID-19 ELISA, and NAb levels were assessed via the GenScript Surrogate Virus Neutralization Test (sVNT). The study included individuals with different vaccination doses and prior infection histories.

RESULTS

the third vaccine dose produced the highest IgG titers, while nonvaccinated individuals and those receiving two doses had lower levels. Prior SARS-CoV-2 infection led to increased antibody levels, suggesting that hybrid immunity offers prolonged protection. The highest NAb titers were observed in individuals receiving three doses, with 96% of previously noninfected individuals being positive for NAb. Risk factor analysis indicated that prior infection (OR = 8.64, 95% CI: 2.52-29.6, p < 0.001) and three doses (OR = 22.1, 95% CI: 2.74-178, p < 0.001) increased immunity.

CONCLUSION

hybrid immunity, involving prior infection and full vaccination, offers enhanced and longer-lasting protection. These results support the need for targeted vaccination strategies to optimize immunity and reduce the risk of adverse outcomes, especially in high-risk populations.