Second Wave of the COVID-19 Pandemic in Delhi, India: High Seroprevalence Not a Deterrent?

Abstract

BackgroundWe report the findings of a large follow-up, community-based, cross-sectional serosurvey and correlate it with the coronavirus disease (COVID-19) test-positivity rate and the caseload observed between the peaks of the first and the second wave of the COVID-19 pandemic in Delhi, India. MethodologyIndividuals aged five and above were recruited from 274 wards of the state (population approximately 19.6 million) from January 11 to January 22, 2021. A total of 100 participants each were included from all wards for a net sample size of approximately 28,000. A multistage sampling technique was employed to select participants for the household serosurvey. Anti-severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) immunoglobulin (IgG) antibodies were detected by using the VITROS® (Ortho Clinical Diagnostics, Raritan, NJ, USA) assay (90% sensitivity, 100% specificity). ResultsAntibody positivity was observed in 14,298 (50.76%) of 28,169 samples. The age, sex, and district population-weighted seroprevalence of the SARS-CoV-2 IgG was 50.52% (95% confidence interval [CI] = 49.94-51.10), and after adjustment for assay characteristics, it was 56.13% (95% CI = 55.49-56.77). On adjusted analysis, participants aged ≥50 years, of female gender, housewives, having ever lived in containment zones, urban slum dwellers, and diabetes or hypertensive patients had significantly higher odds of SARS-CoV-2 antibody positivity.The peak infection rate and the test-positivity rate since October 2020 were initially observed in mid-November 2020, with a subsequent steep declining trend, followed by a period of persistently low case burden lasting until the first week of March 2021. This was followed by a steady increase followed by an exponential surge in infections from April 2021 onward culminating in the second wave of the pandemic. ConclusionsThe presence of infection-induced immunity from SARS-CoV-2 even in more than one in two people can be ineffective in protecting the population. Despite such high seroprevalence, population susceptibility to COVID-19 can be accentuated by variants of concern having the ability for rapid transmission and depletion of antibody levels with the threat of recurrent infections, signifying the need for mass vaccination.

Neutralizing antibody responses to SARS-CoV-2: a population based seroepidemiological analysis in Delhi, India

“…Several population-based SARS-CoV-2 seroepidemiological studies have been conducted in India. However, these studies primarily focussed on screening antibodies in the participants through antibodies recognizing SARS-CoV-2 spike antigens and/or nucleoprotein [5,6].…”

SARS-CoV-2 seroprevalence in Delhi, India - September-October 2021 – a population based seroepidemiological study

“…The weighted and adjusted seroprevalence of IgG SARS-CoV-2 antibodies in Delhi increased from 50.1% and 56.1% in January 2021 to 88.1% and 97%, respectively during September-October 2021 [7]. During the second wave of the countrywide Covid-19 pandemic, Delhi recorded nearly 0.737 million cases including 11075 deaths [2].…”

“…Similar to the trends in previous serosurvey rounds, the seroprevalence was higher in adults compared to children and adolescents, in those having past-history of Covid-19, and in residents of planned colonies in comparison to other settlements. The seropositivity was also significantly higher in females compared to males despite lower rates of vaccination in the former suggesting a biological rather than behavioural phenomenon [6, 7].…”

“…A total of 100 participants each were enrolled from all wards except the Delhi Cantonment and the New Delhi wards. The sample size of approximately 28,000 was estimated at 99% confidence level, 1% absolute precision, 56% expected prevalence from the previous serosurvey [7], design effect of 1.5, and considering a non-response rate of 10%.…”

“…Serial serosurveys previously indicated that the age and sex weighted seroprevalence in Delhi in the ≥5 population increased from 24.71% (95% CI 24.01 to 25.42) in August-October 2020 to 50.52% (95% CI 49.94 to 51.10 in January 2021 [6, 7].…”