SARS-CoV-2 seroprevalence in pregnant women during the first three COVID-19 waves in The Gambia

Abstract Objectives SARS-CoV-2 transmission in Sub-Saharan Africa has probably been underestimated. Population-based seroprevalence studies are needed to determine the extent of transmission in the continent. Methods Blood samples from a cohort of Gambian pregnant women were tested for SARS-CoV-2 total IgM/IgG before ( Pre-pandemic1: October-December 2019 and Pre-pandemic2: February-June 2020) and during the pandemic ( Post-wave1 : October-December 2020, Post-wave2: May-June 2021; and Post-wave3 : October-December 2021). Samples positive for total SARS-CoV-2 IgM/IgG were tested for protein-specific antibodies. Results SARS-CoV-2 total IgM/IgG seroprevalence was 0.9% 95%CI (0.2, 4.9) in Pre-pandemic1 ; 4.1% (1.4, 11.4) in Pre-pandemic2 ; 31.1% (25.2, 37.7) in Post-wave1 ; 62.5% (55.8, 68.8) in Post-wave2 and 90.0% (85.1, 93.5) in Post-wave3. S-protein IgG and NCP-protein IgG seroprevalence also increased at each Post-wave period. Although S-protein IgG and NCP-protein IgG seroprevalence was similar at Post-wave1 , S-protein IgG seroprevalence was higher at Post-wave2 and Post-wave3 , [prevalence difference (PD) 13.5 (0.1, 26.8) and prevalence ratio (PR) 1.5 (1.0, 2.3) in Post-wave2 ; and 22.9 (9.2, 36.6) and 1.4 (1.1, 1.8) in Post-wave3 respectively, p<0.001]. Conclusion SARS-CoV-2 transmission in The Gambia during the first three COVID-19 waves was high, differing significantly from official numbers of COVID-19 cases reported. Our findings are important for policy makers in managing the near-endemic COVID-19. Highlights High specificity of the IgM/IgG SARS-CoV-2 test using samples collected prepandemic Very high (>90%) SARS-CoV-2 seroprevalence after third COVID-19 wave in The Gambia High SARS-CoV-2 transmission contrasts with low number of COVID-19 reported cases