Intense and Mild Wave of COVID-19 in the Gambia: A Cohort Analysis

Abstract

Background. The SARS-CoV-2 pandemic is evolving differently in Africa compared to other regions, with lower transmission and milder clinical presentation. Reasons for this are not fully understood. Recent data from Eastern and Southern Africa suggest that transmission may be higher than measured.Methods. We calculated cumulative rates of SARS-Co-2 infections per 1,000 people at risk in The Gambia (2.42 million individuals) using publicly available data. We evaluated these rates in a cohort of 1,366 employees working at the MRC Unit The Gambia at the London School of Hygiene and Tropical Medicine (MRCG) where systematic surveillance of symptomatic cases and contact tracing was implemented. Cumulative rates among the Gambian population were stratified by age groups and, among the MRCG staff, by occupational exposure risk. SARS-CoV-2 testing was conducted on oropharyngeal/nasopharyngeal samples with consistent sampling and laboratory procedures across cohorts.Findings. By September 2020, 3,579 cases of SARS-CoV-2 and 115 deaths had been identified; with 67% of cases detected in August. Among them, 191 cases were MRCG staff; all of them asymptomatic/mild, with no deaths. The cumulative incidence rate for SARS-CoV-2 infection among MRCG staff (excluding those with occupational exposure risk) was 124 per 1,000 at least 20-fold higher than the estimations based on diagnosed cases in the adult Gambian population.Interpretation. Our findings are consistent with recent Africa sero-prevalence studies reporting high community transmission of SARS-CoV-2. Enhanced community surveillance is essential to further understand and predict the future trajectory of the pandemic in Africa.Funding: Source of funding for the infection control activities and COVID-19 testing at the MRCG are UKRI covid response MC_PC 19061 and European Union COVID-19 response FED/2020/417-470.Conflict of Interest: All authors declare no conflicts of interest.Ethical Approval: National Gambian data was extracted from the publicly available John Hopkins University COVID-19 database(20). Internal databases created for infection control among MRCG staff were anonymized and used to extract MRCG data and as such the study was exempted for ethical approval.