SARS-CoV-2 antibody seroprevalence in unvaccinated medical students, Bamako, Mali: a cross-sectional study by hospital exposure level

BACKGROUND: Medical students are a key group within the healthcare system, yet their risk of SARS-CoV-2 infection remains poorly characterized in Mali. Understanding seroprevalence in this population is essential to inform infection control, vaccination strategies, and decisions regarding in-person training. OBJECTIVE: To assess the seroprevalence of anti-SARS-CoV-2 antibodies among unvaccinated medical students in Bamako, Mali, and to evaluate the association with hospital exposure levels. METHODS: A cross-sectional study was conducted from February to March 2022 among 300 medical students. Participants were stratified by clinical exposure: first-year (pre-clinical), externs, and interns. Blood samples were collected to detect IgA, IgM, and IgG antibodies against SARS-CoV-2 using rapid diagnostic tests, and neutralizing antibodies were assessed in seropositive individuals. Self-reported adherence to barrier measures was recorded. Relative risks (RR) of seropositivity were calculated by exposure level. RESULTS: Overall seroprevalence was 18%, with a clear gradient according to hospital exposure: 12% in first-year students, 17% in externs, and 25% in interns. Compared with first-year students, interns had had an approximately twofold higher risk of having a positive anti–SARS-CoV-2 serology (IgA, IgM, and IgG) compared with first-year students (IgA: RR = 2.18; 95% CI: 1.13–4.21; p = 0.02; IgM: RR = 2.09; 95% CI: 1.08–4.06; p = 0.02; IgG: RR = 2.00; 95% CI: 1.06–3.77; p = 0.03). Compared with externs, interns had a significantly higher prevalence of IgA antibodies (RR = 2.11; 95% CI: 1.0-4.43; p = 0.05). Among seropositive participants, 97.7% had neutralizing antibodies. High self-reported adherence to barrier measures (≈ 93–98%) did not offset the effect of exposure. CONCLUSION: Anti-SARS-CoV-2 seroprevalence among Malian medical students is moderate but exposure-dependent. Results highlight the need for reinforced preventive measures, vaccination prioritization, and ongoing serological surveillance.