SARS-CoV-2 seroprevalence in Delhi, India - 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.

COVID-19 infection, and reinfection, and vaccine effectiveness against symptomatic infection among health care workers in the setting of omicron variant transmission in New Delhi, India

“…All previous SARS CoV-2 seroprevalence surveys in Delhi have reported females in all age groups to have higher odds of seropositivity. 15 , 16 In our study, nurses, resident doctors, faculty/scientists and research staff were most important staff categories that exhibited infection and reinfection during omicron period. This possibly is due to higher risk and gradient of infection exposure while handling patients in service areas by different categories of HCWs.…”

Seroprevalence of immunoglobulin G antibodies against SARS-CoV-2 in children and adolescents in Delhi, India, from January to October 2021: a repeated cross-sectional analysis

“…The high percentage of seroconversion among unvaccinated children and adolescents in this study indicates the presence of natural infection-induced immunity from past exposure to SARS-CoV-2. In comparison, the SARS-CoV-2 IgG seroprevalence in the adult population in Delhi increased from 50.3% (95% CI, 49.7%−51.0%) in January 2021 to 91% (95% CI, 90.6%−91.4%) in September to October 2021 ( Figure 1 ) due to natural infection, COVID-19 vaccination, or hybrid immunity [ 11 , 17 ].…”

“…We tentatively estimated the non-response rate to be <20% based on the feedback provided by the field volunteers and experiences from the previous rounds of the serosurveys. Most population-based seroprevalence studies in India have also reported high non-response rates, especially in the pediatric age group [ 17 , 27 ]. In this study, major reasons for non-response were parental concerns, fear of pain during blood sample collection, and the perceived lack of individual benefit.…”

COVID-19 Vaccine Acceptance and Its Determinants in the General Population of Delhi, India: A State Level Cross-Sectional Survey

“…This cross-sectional analysis reports the ancillary results of a population-based SARS-CoV-2 serosurvey conducted in Delhi from September 24 to October 14, 2021 [ 18 ], a period nearly two and a half months after the end of the second wave of the COVID-19 pandemic in Delhi.…”