Prevalence of SARS-CoV-2 Antibodies From a National Serosurveillance of Kenyan Blood Donors, January-March 2021

High SARS-CoV-2 antibody levels have been achieved in most of the population in high-income countries through vaccination.¹ However, global inequity exists in COVID-19 vaccine distribution, as highlighted at the June 2021 G7 Summit, which committed to providing 1 billion doses to low-income countries. This focus on doses overlooks the pace of transmission in low-income settings.

To monitor seroprevalence in Kenya, we began surveillance of blood donors (aged 16-64 years) in April 2020.^2,3 The national prevalence of SARS-CoV-2 antibodies was estimated at 4.3% in April to June 2020² and 9.1% in August to September 2020.³ In this article we estimate seroprevalence for January to March 2021.

The sampling, laboratory, and analytic methods were identical to those in the studies conducted in 2020.^2,3 Plasma samples with complete donor demographic data and sufficient volume collected from all 6 regional transfusion centers were included and assayed for anti–spike IgG using an enzyme-linked immunosorbent assay. Validated among 910 prepandemic serum samples from coastal Kenya and 174 patients with positive polymerase chain reaction test results from Nairobi, specificity was 99.0% and sensitivity was 92.7%.² Seropositive results were tabulated by age, sex, and region of residence. Donors were stratified into 8 regions by place of residence; these regions are unrelated to the 6 regional transfusion centers, which collate donations across different geographic catchment areas. Bayesian multilevel regression with poststratification using the rjags package in R, version 3.6.1 (R Foundation), was used to obtain seroprevalence estimates and 95% CIs adjusted for the age, sex, and regional distribution of blood donors compared with national data for individuals aged 16 to 64 years based on 2019 census data.^2,3 Adjustment was also done for test performance. The surveillance was approved by the Scientific and Ethics Review Unit of the Kenya Medical Research Institute; written informed consent for use of the data for research was obtained from all donors.

Between January 3, 2021, and March 15, 2021, a total of 3062 samples (median sample date, February 14, 2021) were collected. There were 1145 samples (37.4%) collected from the transfusion center in Nairobi, 879 (28.7%) from Mombasa, 431 (14.1%) from Kisumu, 250 (8.2%) from Embu, 200 (6.5%) from Nakuru, and 157 (5.1%) from Eldoret. Forty-four samples were excluded because of missing information, age-ineligible donors, or collection date before 2021. Of 3018 remaining samples, 1333 were seropositive; crude seroprevalence was 44.2% (95% CI, 42.4%-46.0%) (Table).

The blood donor sample differed from the general population of individuals aged 16 to 64 years (n = 25 954 858) regarding age (8.0% of blood donors were aged 45-64 years vs 19.5% of the population), sex (78.1% of donors were male vs 49.2% of the population), and region (Table). Using bayesian poststratification, the adjusted estimate of seroprevalence among those aged 16 to 64 years in Kenya was 48.5% (95% CI, 45.2%-52.1%). This estimate varied little by age or sex but was higher in Nairobi (61.8% [95% CI, 53.2%-70.6%]), the country’s capital city, and lower in 2 rural regions, Nyanza and Western, adjacent to Uganda.

The prevalence of SARS-CoV-2 antibodies in blood donors in Kenya increased from 4.3%² to 48.5% over 1 year. This is consistent with estimates in other Kenyan populations: 11% among antenatal clinic attendees in rural Kilifi and 50% among clinic attendees in urban Nairobi in August to September 2020³; 42% among truckers in August to November 2020³; and 12% to 13% among health care workers in rural counties and 44% among health care workers in Nairobi in July to December 2020.⁴

Study limitations include that the blood donors were a convenience sample and may not represent the population as a whole, although they have provided useful epidemic intelligence in high-income countries.¹ Although the antibody assay was highly specific in Kenyan prepandemic samples and demonstrated consistent discrimination in a World Health Organization multilaboratory standardization exercise,⁵ sensitivity was estimated in individuals sampled a median of 21 (minimum of 7) days after a positive polymerase chain reaction test result. Antibody concentration and test sensitivity may decline with longer times after infection, implying that seroprevalence may be underestimated by the test-performance adjustment.

These data suggest that SARS-CoV-2 had progressed rapidly across Kenya by February 2021, before a large third wave of infections began in March 2021. Kenya’s COVID-19 vaccine program also began in March 2021 and had reached 2% of the population by July. Natural infection is outpacing vaccine delivery in Kenya, and this reality needs to be considered as objectives of the vaccine program are set.

Corresponding Author: Sophie Uyoga, PhD, Epidemiology and Demography Department, KEMRI-Wellcome Trust Research Programme, PO Box 230, Kilifi, Kenya (suyoga@kemri-wellcome.org).

Accepted for Publication: August 23, 2021.

Published Online: September 2, 2021. doi:10.1001/jama.2021.15265

Correction: This article was corrected on September 24, 2021, to correct an error in which 2 individuals were excluded from the list of Kenya SARS-CoV-2 Serology Consortium members in the Additional Contributions section.

Author Contributions: Drs Uyoga and Scott had full access to all of the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis. Drs Uyoga and Adetifa served as co–first authors and contributed equally to the work and Drs Warimwe and Scott contributed equally to the work.

Concept and design: Uyoga, Adetifa, Yegon, Warimwe, Agweyu, Scott.

Acquisition, analysis, or interpretation of data: All authors.

Drafting of the manuscript: Adetifa, Scott, Otiende.

Critical revision of the manuscript for important intellectual content: Uyoga, Yegon, Warimwe, Agweyu, Scott.

Statistical analysis: Adetifa, Scott, Otiende.

Obtained funding: Adetifa, Warimwe, Agweyu.

Administrative, technical, or material support: Uyoga, Adetifa, Warimwe, Yegon.

Supervision: Adetifa, Warimwe, Scott.

Conflict of Interest Disclosures: Dr Warimwe reported receiving grants from Wellcome Trust during the conduct of the study. Dr Scott reported receiving grants from the Bill and Melinda Gates Foundation, the UK Foreign Commonwealth and Development Office, and Wellcome Trust during the conduct of the study and grants from Gavi, the Vaccine Alliance, the National Institute for Health Research, and the Medical Reserve Corps outside the submitted work. No other disclosures were reported.

Funding/Support: This work was supported by the Bill and Melinda Gates Foundation (INV-017547), the Foreign Commonwealth and Development Office, and Wellcome Trust (grants 220991/Z/20/Z, 203077/Z/16/Z).

Role of the Funder/Sponsor: The funding agencies had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.

Data Sharing Statement: The data shown in the article are available on request from the corresponding author. Deidentified data have been published on the Harvard Dataverse server (https://doi.org/10.7910/DVN/FQUNVD).

Disclaimer: This study has been published with the permission of the director of the Kenya Medical Research Institute. The director played no role in deciding whether to submit the manuscript for publication nor the journals to which to submit.

Additional Contributions: We thank all the blood donors for their contribution to the research. Members of the Kenya SARS-CoV-2 Serology Consortium are James Nyagwange, PhD; Henry K. Karanja, MSc; James Tuju, PhD; John Gitonga, Dip; Daisy Mugo, BSc; Johnstone Makale, BSc; Eunice W. Kagucia, PhD; Katherine E. Gallagher, PhD; Anthony Etyang, PhD; Shirine Voller, MSc; Edwine Barasa, PhD; Benjamin Tsofa, PhD; Philip Bejon, PhD; Lynette I. Ochola-Oyier, PhD (KEMRI-Wellcome Trust Research Programme, Kilifi, Kenya); Rashid Aman, PhD; Mercy Mwangangi, MSc; Patrick Amoth, MMed; Kadondi Kasera, MSc (Ministry of Health, Nairobi, Kenya); Wangari Ng’ang’a, MSc; (Presidential Policy & Strategy Unit, The Presidency, Government of Kenya), Nduku Kilonzo, PhD; Evelynn Chege, MMed; Elizabeth Odhiambo, BSc; Thomas Rotich, BSc; Irene Orgut, BSc; Sammy Kihara, Dip (Kenya National Blood Transfusion Services, Nairobi Kenya); Christian Bottomley, PhD (London School of Hygiene & Tropical Medicine, London, UK); Teresa Lambe PhD; and Daniel Wright, MSc (Nuffield Department of Clinical Medicine, Oxford University, Oxford, UK).