Serological Profile of SARS-CoV-2 IgG Antibodies in Vaccinated and Unvaccinated Hospital Workers in Dakar, Senegal

Background: The COVID-19 pandemic placed hospital workers at the front line of viral exposure, raising critical questions about the magnitude and durability of vaccine-induced humoral immunity in this population. Limited data are available on the serological response to SARS-CoV-2 vaccines among health-care workers in sub-Saharan Africa, particularly in Senegal where the AstraZeneca and Sinopharm vaccines were the main platforms deployed. Objective: To assess the serological profile of SARS-CoV-2 IgG antibodies in vaccinated and unvaccinated staff of the Idrissa Pouye General Hospital (HOGIP) in Dakar, Senegal, and to identify epidemiological factors associated with anti-RBD IgG seropositivity. Methods: A descriptive and analytical study was conducted from January 2022 to January 2023, enrolling 61 hospital workers (52 vaccinated with at least two doses of the COVID-19 vaccine AstraZeneca or Sinopharm COVID-19 vaccine; 9 unvaccinated controls). Quantitative anti-SARS-CoV-2 IgG antibodies targeting the receptor-binding domain (RBD) of the spike protein were measured by chemiluminescent microparticle immunoassay (CMIA, AdviseDx SARS-CoV-2 IgG II, Abbott) on the ARCHITECT ci4100 analyzer anti-RBD IgG seropositivity was defined as an IgG titer ≥ 50 AU/mL. Non-parametric tests (Mann-Whitney, Kruskal-Wallis, Spearman) were used; p < 0.05 was considered significant. Results: anti-RBD IgG seropositivity was observed in 98% of vaccinated participants and 100% of unvaccinated participants. Median IgG titers were 4671.8 AU/mL with AstraZeneca, 3177.5 AU/mL with Sinopharm and 1408 AU/mL in unvaccinated controls. Vaccination status (p < 0.05) and age (Spearman ρ = 0.39, p = 0.002) were the only factors significantly associated with antibody titers. Sex, comorbidities, vaccine type and inter-dose interval had no significant effect. Conclusion: Hospital workers at HOGIP showed high humoral immunity to SARS-CoV-2 regardless of vaccination, suggesting widespread occult exposure on top of vaccine-induced responses. Vaccination and age were the main determinants of antibody titers.