ABSTRACT
BackgroundWe 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. MethodsThis 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(R) (Ortho Clinical Diagnostics, Raritan, NJ, USA) assay (90% sensitivity, 100% specificity). ResultsA 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 O_TBL View this table: org.highwire.dtl.DTLVardef@1482d5forg.highwire.dtl.DTLVardef@19ab8a1org.highwire.dtl.DTLVardef@cf675dorg.highwire.dtl.DTLVardef@8b427aorg.highwire.dtl.DTLVardef@b96a54_HPS_FORMAT_FIGEXP M_TBL O_FLOATNOTable 4.C_FLOATNO O_TABLECAPTIONVaccination status and seroprevalence of antibodies to SARS-CoV-2, Delhi, September-October 2021* C_TABLECAPTION C_TBL ConclusionsWe observed IgG antibodies against SARS-CoV-2 in most of the general population of Delhi with likely higher antibody titres in the vaccinated compared to the unvaccinated groups.
