SARS‐CoV‐2 seroprevalence and implications for population immunity: Evidence from two Health and Demographic Surveillance System sites in Kenya, February–December 2022.

Background: We sought to estimate SARS‐CoV‐2 antibody seroprevalence within representative samples of the Kenyan population during the third year of the COVID‐19 pandemic and the second year of COVID‐19 vaccine use. Methods: We conducted cross‐sectional serosurveys among randomly selected, age‐stratified samples of Health and Demographic Surveillance System (HDSS) residents in Kilifi and Nairobi. Anti‐spike (anti‐S) immunoglobulin G (IgG) serostatus was measured using a validated in‐house ELISA and antibody concentrations estimated with reference to the WHO International Standard for anti‐SARS‐CoV‐2 immunoglobulin. Results: HDSS residents were sampled in February–June 2022 (Kilifi HDSS N = 852; Nairobi Urban HDSS N = 851) and in August–December 2022 (N = 850 for both sites). Population‐weighted coverage for ≥1 doses of COVID‐19 vaccine were 11.1% (9.1–13.2%) among Kilifi HDSS residents by November 2022 and 34.2% (30.7–37.6%) among Nairobi Urban HDSS residents by December 2022. Population‐weighted anti‐S IgG seroprevalence among Kilifi HDSS residents increased from 69.1% (65.8–72.3%) by May 2022 to 77.4% (74.4–80.2%) by November 2022. Within the Nairobi Urban HDSS, seroprevalence by June 2022 was 88.5% (86.1–90.6%), comparable with seroprevalence by December 2022 (92.2%; 90.2–93.9%). For both surveys, seroprevalence was significantly lower among Kilifi HDSS residents than among Nairobi Urban HDSS residents, as were antibody concentrations (p < 0.001). Conclusion: More than 70% of Kilifi residents and 90% of Nairobi residents were seropositive for anti‐S IgG by the end of 2022. There is a potential immunity gap in rural Kenya; implementation of interventions to improve COVID‐19 vaccine uptake among sub‐groups at increased risk of severe COVID‐19 in rural settings is recommended. [ABSTRACT FROM AUTHOR]