SARS-CoV-2 seroprevalence among pregnant women during the first three waves of the COVID-19 pandemic in southern Mozambique

COVID-19 in pregnancy is associated with complications for mother and baby (e.g., maternal admission to intensive care, preterm birth). There is little evidence on the prevalence of SARS-CoV-2 in pregnant women from Sub-Saharan Africa. Most studies used a small sample size within a short period and did not accurately assess prevalence as the pandemic progressed. This study aimed to determine the maternal seroprevalence of SARS-CoV-2 from the beginning of the pandemic until the end of the third wave in southern Mozambique. This study was nested in the PRECISE study, a prospective observational cohort study of pregnant women enrolled at first antenatal care and followed up until delivery in The Gambia, Kenya, and Mozambique. For this study, samples were evaluated from October 2019 to March 2022 in Mozambique. Serum from all mothers (using Wantai SARS-CoV-2 Ab ELISA) and cord blood from a random sample of SARS-CoV-2 positive mothers (by the Euroimmun test) were tested. The seroprevalence was calculated as proportions with 95% confidence intervals (CIs). Bivariate logistic regression was used to test associations between the presence of SARS-CoV-2 antibodies and the time and place of sample collection, with p-value < 0.05 considered statistically significant. From PRECISE Mozambique, 2080 women contributed 3392 samples, 1651 at the time of antenatal recruitment and 1741 on admission for delivery. The mean seroprevalence in the tested samples was 26.2% and varied from 4.9% 95% CI 2.4–8.9 pre-pandemic to 82% 95% CI 71.8–90.3 after the third wave. In a subsample of 215 mothers Wantai seropositive, seroprevalence by Euroimmun was 47.4% in maternal serum and 40.9% in cord blood. Except for the first wave, where the prevalence in maternal serum was high, there were no differences in prevalence in maternal serum and cord blood among the waves. The study reported a rising seroprevalence for antibodies to SARS-CoV-2 in pregnancy, particularly in the third wave when the Omicron variant predominated. In a subsample, the prevalence of SARS-CoV-2 in maternal serum was similar to that in cord blood, indicating good antibody transfer from mother to child. We found positivity with the Wantai test in the pre-pandemic period but not with Euroimmun, indicating the need for test validation in different geographies and contexts.