Seroprevalence of COVID-19 infection among vaccine naïve population after the second surge (June 2020) in a rural district of South India: A community-based cross-sectional study

Abstract

Objective To determine the seroprevalence of the SARS Cov 2 infection among vaccine naive population in a rural district of South India post-second surge. Methodology We conducted a cross-sectional study in the five villages of a randomly chosen sub-district in the Bangalore rural district. We did house to house surveys and recruited 831 vaccine naive adults in July 2021. We tested samples for the presence of antibodies (including IgG & IgM) to SARS CoV-2 using the Roche Elecsys SARS-CoV-2 –S assay that quantifies antibodies against the receptor-binding domain (RBD) of the spike (S) protein. Results We estimated an overall prevalence of 62.7% (95% CI: 59.3–66.0) and an age-and gender-adjusted seroprevalence of 44.9% (95% CI: 42.5–47.4). When adjusted for test performance, the seroprevalence was 74.64% (95% CI: 70.66–78.47). The case-to-undetected-infected ratio (CIR) was 1: 8.65 (95% CI 1:8.1–1:9.1), and the Infection Fatality Rate (IFR) was 16.27 per 100,00 infections as of 13 July 2021. A history of at least one symptom suggestive of COVID-19 or a positive COVID-19 test of self or a family member in the past were significantly associated with seropositivity. Conclusion We report a high seroprevalence of COVID-19 infection despite the advantages of low population density and well-ventilated landscapes in rural areas. CIR and IFR were higher than the previous serosurvey conducted in the same population during the first surge. The thought of achieving herd immunity comes with relief. However, it’s vital to put efforts into building population health and rural health infrastructure to avert future health catastrophes.