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