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

Objectives To assess seroprevalence of anti-SARS-CoV-2 antibodies in a densely populated urban Indian settings and its implications for disease trends and protective immunity. Design Cross-sectional sero-epidemiological survey linked with administrative reporting of COVID-19 testing data. Settings Pune city in western India Main outcome measure Prevalence of anti-SARS-CoV-2 spike protein antibodies were estimated and along with correlates of virus neutralisation and other immune and inflammatory markers. Results Seropositivity was extensive (51·3%; 95%CI 39·9 to 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 0.21%. 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. Conclusion 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. It is also supported by substantial neutralising activity in asymptomatically infected individuals. This is the first report of a significantly high proportion of protective immune response among asymptomatic individuals in the population. The heterogeneity in antibody levels and neutralisation capacity indicates the existence of immunological sub-groups of functional interest. Trial registration Registered with the Clinical Trials Registry of India (CTRI/2020/07/026509) ### Competing Interest Statement The authors have declared no competing interest. ### Clinical Trial CTRI/2020/07/026509 ### Funding Statement The study was supported by the Persistent Foundation, Pune, India. The funding agency had no involvement in any aspect of the study. No other funding has been received by the authors or their institutions regarding this study. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: The study was approved by the Institutional Ethics Committee of SPPU (SPPU/IEC/2020/82), IISER Pune (IECHR/Admin/2020/005) and THSTI (THS1.8.1(106)) All necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable. Yes All data is available on reasonable request.