SARS-CoV-2 antibody prevalence in Sierra Leone, March 2021: a cross-sectional, nationally representative, age-stratified serosurvey

ABSTRACT

Introduction/ Background: As of March 2021, the Africa CDC had reported 4,159,055 cases of COVID-19 and 111,357 deaths among the 55 African Union Member States;however, no country has published a nationally representative serosurvey. Such data are vital for understanding the pandemic's progression on the continent, evaluating containment measures, and policy planning. Methods: We conducted a cross-sectional, nationally representative, age-stratified serosurvey in Sierra Leone in March 2021 by randomly selecting 120 Enumeration Areas throughout the country and 10 randomly selected households in each of these. One to two persons per selected household were interviewed to collect information on sociodemographics, symptoms suggestive of COVID-19, exposure history to laboratory-confirmed COVID-19 cases, and history of COVID-19 illness. Capillary blood was collected by fingerstick, and blood samples were tested using the Hangzhou Biotest Biotech RightSign COVID-19 IgG/IgM Rapid Test Cassette. Total seroprevalence was estimated after applying sampling weights. Results: The overall weighted seroprevalence was 2.6% (95% CI 1.9-3.4). This was 43 times higher than the reported number of cases. Rural seropositivity was 1.8% (95% CI 1.0-2.5), and urban seropositivity was 4.2% (95% CI 2.6-5.7). Stratifying by age group and weighting, 1.7% (95% CI 0.2-3.2) of participants age 5-9 tested positive for anti-SARS-CoV-2 antibodies, as did 2.6% (95% CI 0.8- 4.2) of those 10-19, 1.2% (95% 0.2-2.3) of those 20-39, 4.4% (95% CI 2.4-6.4) of those 40-59, and 3.6% (95% CI 1.6-5.6) of those 60 and above. There was a significant difference in seropositivity between rural/urban populations (Rao-Scott Chi-square p=0.002). Impact This has ramifications for the country's third wave, where the average number of daily reported cases was 87 by the end of the Jone 2021-this could potentially be on the order of 3,700 actual infections, calling for stronger containment measures in a country with only 0.2% of people fully vaccinated. Conclusion: Overall seroprevalence was low compared to countries in Europe and the Americas (suggesting relatively successful containment in Sierra Leone). The results may reflect significant underreporting of incidence and mortality across the continent.