Phased Multi-Country Seroepidemiology Study of Over 20000 Individuals In West Africa Reveals the Dynamics of SARS-CoV-2 Exposure Driven by Delta, Omicron and Omicron Waves

Background: Africa has appeared spared from severe morbidity and mortality upon SARS-COV-2 infection. Studies have demonstrated high-level SARS-CoV-2 seropositivity in healthy Africans, which some have attributed to pre-pandemic cross-reactive antibodies. Phased studies can link trends in SARS-CoV-2 seropositivity to transmission waves. This study tracked trends in seropositivity across three West African countries and investigated factors associated with seropositivity, vaccine uptake and attitudes. Methods: Phased serosurveys were conducted across three West African countries: Burkina Faso, Ghana, and Nigeria. SARS-CoV-2 antibodies were detected in peripheral blood using validated immunoassay kits. Sampling periods correlated to ‘Delta’ and ‘Omicron’ waves. The primary outcome was the proportions of each population that have antibodies to SARS-CoV-2. Participants’ metadata was obtained using a semi-structured questionnaire. Findings: Participants numbered 20,748 across the 3 countries. Across countries, SARS-CoV-2 IgG seropositivity ranged from 24.1-77.0 %. Seropositivity was higher than in previous Ghanaian ‘Alpha wave’ studies. At all sites, seropositivity increased sharply during the ‘Omicron’ wave, indicating that seropositivity was likely linked to increased transmissions. All sites demonstrated low self-reported vaccination rates, delinking seropositivity and vaccination. There was a significant positive association between seropositivity and age across all sites. Association with other demographic factors was country dependent. Most participants expressed positive opinions of vaccination; negative opinions often reflected misinformation. Significance: This, the largest population-based SARS-CoV-2 seroepidemiology study in Africa, confirms widespread exposure to SARS-CoV-2 infection in West Africa, not linked to pre-existing cross-reactivity. This study supports population-level biological protection against severe COVID-19 in West Africa. Funding: The Rockefeller Foundation, UK government Foreign Commonwealth Development Office (FCDO) and the Agence Française de Développement (AFD).Declaration of Interest: Authors have no conflicts of interest to declare.Ethical Approval: Approval was received in Ghana from the Ethics Board of the College of Basic and Applied Sciences, University of Ghana (ECBAS 063/19–20), and the Ethics Review Committee of the Ghana Health Service (GHS-ERC 011/03/20). Procedures in the study conformed with the Ghanaian Public Health Act, 2012 (Act 851) and the Data Protection Act, 2012 (Act 843). In Nigeria, ethical approval was from the National Health Research Ethics Committee (NHREC/17/03/2018 and NHREC/01/01/2007). Ethical approval for the study in Burkina Faso was from the Government. Additional approval was sought from local authorities at all sampling sites included in the study. Written informed consent was obtained according to the Helsinki Declaration from participants before questionnaire administration, sample collection and testing. Minors (under18 years) were enrolled following written consent from their parent/legal guardian. Written assent was also sought from children 10–18 years old before enrolment in the study.