A Descriptive Study of Community based Seroprevalence of SARS-CoV2 antibodies among adult population in Mumbai, India using an ELISA based assay

Abstract

Background: Mumbai, with over 12 million residents, is one of the largest cities in India and the capital of the state of Maharashtra that accounted for close to 20% of the total COVID-19 cases in India. Regular serosurveys in Mumbai have shown stark differences in seroprevalence between slum and non-slum areas. The present study aimed to evaluate the prevalence of SARS-CoV-2 antibodies in Mumbai residents and assess the impact of the second wave and ongoing vaccination campaign on the population antibodies. By the start of the study period, 63% of Mumbai residents were partially vaccinated and 21% were fully vaccinated for COVID-19. Methods: We conducted a cross-sectional seroprevalence study in all 24 wards of Mumbai between August 12 and September 08, 2021. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibody seropositivity was detected using an ELISA based assay. Sociodemographic and exposure related data was collected via a verbal questionnaire to analyse risk factors and association with COVID-19 vaccination. Findings: Of the 8,674 participants recruited, 7,516 were positive for IgG SARS-COV-2, resulting in a crude seroprevalence of 86.6%. Using residence type based on the recruitment location (municipal dispensaries for slum residents and general practitioners for non-slum residents), the difference in prevalence between slum and non-slum is not significant (87.0% vs. 86.2%; RR: 1.009, CI: 0.992-1.026). Seroprevalence was higher in females (88.3%) than in males (85.1%) (RR: 096, CI 95%: 0.94-0.97) Conclusion: Our results suggest that the levels of immunity are high in the Mumbai population across residence types. These findings highlight the extent of virus transmission during the second wave and point to the susceptible population to guide the vaccination strategy and better understand transmission dynamics in urban settings.