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

• Authors: Isaac Ngere, Washington State University; Jeanette Dawa, Washington State University; Elizabeth Hunsperger, US Centers for Disease Control and Prevention (CDC)-Kenya; Nancy Otieno, Kenya Medical Research Institute (KEMRI); Moses Masika, University of Nairobi; Patrick Amoth, Kenya Ministry of Health; Lyndah Makayotto, Nairobi Metropolitan Services; Carolyne Nasimiyu, Washington State University; Bronwyn M Gunn, Washington State University; Bryan Nyawanda, Kenya Medical Research Institute (KEMRI); Ouma Oluga, Nairobi Metropolitan Services; Carolyne Ngunu, Nairobi Metropolitan Services; Harriet Mirieri, Washington State University; John Gachohi, Washington State University; Doris Marwanga, Washington State University; Patrick K Munywoki, US Centers for Disease Control and Prevention (CDC)-Kenya; Dennis Odhiambo, Kenya Medical Research Institute (KEMRI); Moshe D Alando, Kenya Medical Research Institute (KEMRI); Robert Breiman, Emory University; Omu Anzala, University of Nairobi; Kariuki M Njenga, Washington State University; Marc Bulterys, US Centers for Disease Control and Prevention (CDC)-Kenya; Amy Herman-Roloff, US Centers for Disease Control and Prevention (CDC)-Kenya; Eric Osoro, Washington State University
• Journal Title: INTERNATIONAL JOURNAL OF INFECTIOUS DISEASES
• Volume: Volume 112
• Publisher: ELSEVIER SCI LTD | 2021-09-30, Pages 25-34
• Type of Work: Article | Final Publisher PDF
• Publisher DOI: http://doi.org/10.1016/j.ijid.2021.08.062
• Subjects: Health Sciences, Public Health
• Keywords: Science & Technology; Life Sciences & Biomedicine; Infectious Diseases; COVID-19 pandemic; SARS-CoV-2; Seroprevalence; Disease underreporting; Infection underestimation; ANTIBODY

Abstract

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 structure 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 populated 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 100,000 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.