This is a summary, written by members of the CITF Secretariat, of:
Lewis HC, Ware H, Whelan M, Subissi L, Li Z, Ma X, Nardone A, Valenciano M, Cheng B, Noel K, Cao C, Yanes-Lane M, Herring BL, Talisuna A, Ngoy N, Balde T, Clifton D, Van Kerkhove MD, Buckeridge D, Bobrovitz N, Okeibunor J, Arora RK, Bergeri I; UNITY Studies Collaborator Group. SARS-CoV-2 infection in Africa: a systematic review and meta-analysis of standardised seroprevalence studies, from January 2020 to December 2021. BMJ Glob Health. 2022 Aug;7(8):e008793. doi: 10.1136/bmjgh-2022-008793.
The results and/or conclusions contained in the research do not necessarily reflect the views of all CITF members
In a systemic review published in BMJ Global Health, Dr. Rahul Arora (University of Calgary) and the CITF-funded SeroTracker team estimates that seroprevalence in Africa (due to infection or vaccination) was 65.1% in July-September 2021. This seroprevalence estimate suggests there were 100 times more infections than the number reported to the WHO by national surveillance systems, highlighting that most infections go undetected.
Researchers calculated ratios of actual to reported infections to assess the extent to which the true disease burden is underestimated. The number of actual infections was derived by applying meta-analyzed infection-acquired seroprevalence estimates to the African population. Reported infections correspond to the number of laboratory-confirmed cases reported by national surveillance systems to the World Health Organization (WHO).
- Seroprevalence (due to infection or vaccination) increased from 3% in April-June 2020 to 65.1% by July-September 2021 in Africa.
- Ratios of estimated actual to reported infections ranged from 18:1 in South Africa to 954:1 in Nigeria, showing great inter-country heterogeneity.
- Asymptomatic cases in Africa are estimated to represent 71.0% of all cases. These findings are consistent with other studies showing particularly high rates of asymptomatic infection in Africa (between 65% and 85% according to the World Health Organization Regional Office for Africa). Infected individuals without symptoms on this continent have been unlikely to seek testing, which might partly explain the under-ascertainment of SARS-CoV-2 infections.
- Seroprevalence was found to vary by region and age. Seroprevalence was 40% lower in rural areas compared with urban areas. Seroprevalence was 27% lower in children aged 0-9 years compared with adults aged 20-29 years.
The heterogeneity of estimates within and between countries also underscores the importance of adapting public health measures and vaccination strategies to specific local contexts.
A total of 56 full texts, comprising 153 distinct seroprevalence studies conducted in Africa and published from January 1, 2020 to December 30, 2021, were included as part of the systematic review. The estimate of asymptomatic seroprevalence (i.e., the proportion of seropositive individuals that reported no COVID-19 symptoms during the study period) is based on a subset of the 15 studies that reported symptoms.
The studies cover African member states of the World Health Organization, representing more than 40% (23/54) of the continent, as a result of the standardization and adaptability of the WHO UNITY Studies. This study is the first to provide such robust and representative seroprevalence estimates in Africa.
The significant under-ascertainment of SARS-CoV-2 infections and its high heterogeneity underscores the need for timely seroprevalence data and continued surveillance of susceptible populations to guide public health priorities. This review was conducted in partnership between the CITF-funded SeroTracker initiative and the WHO’s UNITY initiative, through which the quantity and quality of available seroprevalence data in Africa has increased.