High seroprevalence of SARS-CoV-2 but low infection fatality ratio eight months after introduction in Nairobi, Kenya

Background: The lower than expected COVID-19 morbidity and mortality in Africa has been attributed to multiple factors, including weak surveillance. This study estimated the burden of SARS-CoV-2 infections eight months into the epidemic in Nairobi, Kenya. Methods: A population-based, cross-sectional survey was conducted using multi-stage random sampling to select households within Nairobi in November 2020. Sera from consenting household members were tested for antibodies to SARS-CoV-2. Seroprevalence was estimated after adjusting for population struc-ture and test performance. Infection fatality ratios (IFRs) were calculated by comparing study estimates with reported cases and deaths. Results: Among 1,164 individuals, the adjusted seroprevalence was 34.7% (95% CI 31.8-37.6). Half of the enrolled households had at least one positive participant. Seropositivity increased in more densely pop-ulated areas (spearman's r = 0.63; p = 0.009). Individuals aged 20-59 years had at least two-fold higher seropositivity than those aged 0-9 years. The IFR was 40 per 10 0,0 0 0 infections, with individuals >= 60 years old having higher IFRs. Conclusion: Over one-third of Nairobi residents had been exposed to SARS-CoV-2 by November 2020, indicating extensive transmission. However, the IFR was > 10-fold lower than that reported in Europe and the USA, supporting the perceived lower morbidity and mortality in sub-Saharan Africa. (C) 2021 The Author(s). Published by Elsevier Ltd on behalf of International Society for Infectious Diseases.

Automated summary

This study in Nairobi, Kenya estimated that over one-third of residents had been exposed to SARS-CoV-2 by November 2020, with seropositivity increasing in more densely populated areas. The infection fatality ratios (IFRs) also increased with age, being higher for individuals aged 60 years and older.