Abstract

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

Lucinde, R. K. Mugo, D. Bottomley, C. Karani, A. Gardiner, E. Aziza, R. Gitonga, J. N. Karanja, H. Nyagwange, J. Tuju, J. Wanjiku, P. Nzomo, E. Kamuri, E. Thuranira, K. Agunda, S. Nyutu, G. Etyang, A. O. Adetifa, I. M. O. Kagucia, E. Uyoga, S. Otiende, M. Otieno, E. Ndwiga, L. Agoti, C. N. Aman, R. A. Mwangangi, M. Amoth, P. Kasera, K. Nyaguara, A. Ng'ang'a, W. Ochola, L. B. Namdala, E. Gaunya, O. Okuku, R. Barasa, E. Bejon, P. Tsofa, B. Ochola-Oyier, L. I. Warimwe, G. M. Agweyu, A. Scott, J. A. G. Gallagher, K. E.
PLoS One. 2022; 17e0265478

Permanent descriptor

https://doi.org/10.1371/journal.pone.0265478

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.