Community prevalence of antibodies to SARS-CoV-2 and correlates of protective immunity in five localities in an Indian metropolitan city

Ghose, A.; Bhattacharya, S.; Karthikeyan, A. S.; Kudale, A. M.; Monteiro, J. M.; Joshi, A.; Medigeshi, G. R.; Kang, G.; Bal, V.; Rath, S.; Shashidhara, L. S.; John, J.; Chaudhuri, S.; Nagarkar, A.

Background Current testing guidelines for COVID-19 substantially underestimates the spread of SARS-CoV-2 in dense urban populations. Granular estimates of infection are important for understanding population-level immunity. We examined seroprevalence of anti-SARS-CoV-2 antibodies in Pune city in India and its implication for protective immunity. Methods Seroprevalence was estimated during July 20-August 5, 2020 from 1659 randomly selected individuals recruited from five administrative Pune sub-wards (combined population 366,984). Prevalence of anti-SARS-CoV-2 spike protein antibodies were estimated and along with correlates of virus neutralisation. Findings Seropositivity was extensive (51.3%; 95%CI 39.9-62.4) but varied widely in the five localities tested, ranging from 35.8% to 66.4%. Seropositivity was higher in crowded living conditions in the slums (OR 1.91), and was lower in those 65 years or older (OR 0.59). The infection-fatality ratio was estimated at 0.28%. Post survey, COVID-19 incidence was lower in areas noted to have higher seroprevalence. Substantial virus-neutralising activity was observed in seropositive individuals, but with considerable heterogeneity in the immune response and possible age-dependent diversity in the antibody repertoire. Interpretation Despite crowded living conditions having facilitated widespread transmission, the variability in seroprevalence in localities that are in geographical proximity indicates a heterogenous spread of infection. Declining infection rates in areas with high seropositivity suggest population-level protection and is supported by substantial neutralising activity in asymptomatically infected individuals. The heterogeneity in antibody levels and neutralisation capacity indicates the existence of immunological sub-groups of functional interest.