SARS-CoV-2 Seroprevalence in Delhi, India, During September-October 2021: A Population-Based Seroepidemiological Study

Abstract

Background We conducted a repeat serosurvey in Delhi, India to estimate the seroprevalence of SARS-CoV-2 in the general population and compare the antibody prevalence in the vaccinated and non-vaccinated groups. Methods This cross sectional study was conducted from September 24 to October 14 2021 in 280 wards of Delhi among 27811 participants selected through a multistage sampling technique with housing settlement based stratification. The SARS-CoV-2 immunoglobulin (IgG) antibodies were screened with the VITROS (Ortho Clinical Diagnostics, Raritan, NJ, USA) assay (90% sensitivity, 100% specificity). Results A total of 24895 (89.5%) samples were seropositive. The crude seroprevalence was 87.99% (95% CI 89.1, 89.8), weighted for age and sex was 88% (95% CI 87.6, 88.4), and after adjustment of assay performance was estimated as 97.5% (95% CI 97.0, 98.0). The weighted seroprevalence in the 11 districts ranged from 84.9% (South-West district) to 90.8% (East district) Females in all the age-groups (<18, 18-49 and ≥50) had significantly higher odds of seropositivity (p<0.001). On adjusted analysis, the odds of seroconversion in the participants vaccinated with at-least one dose of either Covid-19 vaccine (Covishield/Covaxin) was more than four times compared to the unvaccinated (aRR 4.2 (3.8, 4.6)). The seroprevalence was also comparable among the complete and partially vaccinated subgroups for both vaccines (Table 4). Most (86.8%) seropositive individuals had a SARS-CoV-2 signal/cut-off ≥4.0 except in children Conclusions We observed IgG antibodies against SARS-CoV-2 in most of the general population of Delhi with likely higher antibody titers in the vaccinated compared to the unvaccinated groups.Competing Interest StatementThe authors have declared no competing interest.Funding StatementThis research received no specific funding from any agency in the public, commercial or not-for-profit sectors. The logistics and human resources were deputed by the Directorate General of Health Services, government of the National Capital Territory, Delhi and supported by the ATE Chandra Foundation and ACT grants. Author DeclarationsI confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.YesThe 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, Maulana Azad Medical College & Associated Hospitals, New Delhi vide F.1/IEC/MAMC/85/03/2021/No428 dated 21.08.2021I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals.YesI 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.YesAll data produced in the present study are available upon reasonable request to the authors