Sero-surveillance for IgG to SARS-CoV-2 at antenatal care clinics in three Kenyan referral hospitals: Repeated cross-sectional surveys 2020–21

Abstract

Introduction The high proportion of SARS-CoV-2 infections that have remained undetected presents a challenge to tracking the progress of the pandemic and estimating the extent of population immunity. Methods We used residual blood samples from women attending antenatal care services at three hospitals in Kenya between August 2020 and October 2021and a validated IgG ELISA for SARS-Cov-2 spike protein and adjusted the results for assay sensitivity and specificity. We fitted a two-component mixture model as an alternative to the threshold analysis to estimate of the proportion of individuals with past SARS-CoV-2 infection. Results We estimated seroprevalence in 2,981 women; 706 in Nairobi, 567 in Busia and 1,708 in Kilifi. By October 2021, 13% of participants were vaccinated (at least one dose) in Nairobi, 2% in Busia. Adjusted seroprevalence rose in all sites; from 50% (95%CI 42–58) in August 2020, to 85% (95%CI 78–92) in October 2021 in Nairobi; from 31% (95%CI 25–37) in May 2021 to 71% (95%CI 64–77) in October 2021 in Busia; and from 1% (95% CI 0–3) in September 2020 to 63% (95% CI 56–69) in October 2021 in Kilifi. Mixture modelling, suggests adjusted cross-sectional prevalence estimates are underestimates; seroprevalence in October 2021 could be 74% in Busia and 72% in Kilifi. Conclusions There has been substantial, unobserved transmission of SARS-CoV-2 in Nairobi, Busia and Kilifi Counties. Due to the length of time since the beginning of the pandemic, repeated cross-sectional surveys are now difficult to interpret without the use of models to account for antibody waning.

Comparison of nucleocapsid and spike antibody ELISAs for determining SARS‐CoV‐2 seropositivity in Kenyan women and infants

“…Nucleocapsid and spike‐antigen ELISAs have been used to study SARS‐CoV‐2 seroprevalence among specific groups in Kenya, such as blood donors, truck drivers, healthcare workers, and antenatal clinic attendees 14–17 . The Mount Sinai ELISA, which has been shown to demonstrate high specificity and sensitivity to the receptor‐binding domain (RBD) and spike antigens, received US FDA Emergency Use Authorization (EUA) in 2020 and has been independently validated for use in Kenyan populations 17–19 .…”

Seroepidemiology of SARS-CoV-2 in a cohort of pregnant women and their infants in Uganda and Malawi

“…Studies included in a systematic review and meta-analysis of anti-SARS-CoV-2 seroprevalence in Africa showed wide-variation between countries (seroprevalence estimates ranged from 0% to 63%) [21]. A study of antenatal care clinics in two Kenyan referral hospitals found highest seroprevalence of up to 85% in Busia [22]. Our data indicates that the majority of cases were asymptomatic and adds to existing evidence that suggests under-reporting of infection if based solely on confirmed cases by PCR [4,5,21].…”

Trends in SARS-CoV-2 seroprevalence among pregnant women attending first antenatal care visits in Zambia: a repeated cross-sectional survey, 2021-2022

“…10 Repeated cross-sectional serosurveys in ANC clinics in Kenya found that most women were seropositive for SARS-CoV-2 antibodies by October 2021. 11 Early SARS-CoV-2 serosurveys measured antibodies to estimate total infections, but COVID-19 vaccine rollout now clouds seroprevalence interpretations. Detectable antibodies may be the result of SARS-CoV-2 infection, COVID-19 vaccination, or both.…”

“…10 Repeated cross-sectional serosurveys in ANC clinics in Kenya found that most women were seropositive for SARS-CoV-2 antibodies by October 2021. 11…”