Murhekar MV, Bhatnagar T, Thangaraj JWV, et al. - In earlier nationwide COVID-19 serosurveys, seroprevalence was identified to have increased from 0.73% in May–June 2020 to 6.6% in September–October 2020 and 24.1% in December 2020–January 2021. In January 2021, COVID-19 vaccination began in India, initially targeting healthcare and frontline workers. Expansion of the vaccination strategy took place in a phased manner and currently all individuals aged 18 years and above are covered. This is the fourth nationwide serosurvey conducted with the aim to determine the prevalence of SARS-CoV-2 antibodies in the general population aged ≥ 6 years and healthcare workers (HCWs).

• Between 14 June and 6 July 2021, this cross-sectional study was conducted in the same 70 districts across 20 states and 1 union territory where researchers had conducted 3 previous rounds of serosurveys.

• For inclusion, a total of 10 clusters (villages in rural areas and wards in urban areas) were selected from each district, with a minimum of 400 individuals aged ≥ 6 years from the general population (40 individuals from each cluster) and 100 HCWs from the district public health facilities.

• Antibodies against SARS-CoV-2 were present in nearly two-thirds of India’s population aged ≥ 6 years by June–July 2021.

• There was an increase in seroprevalence with age, but no difference was observed in urban slum, urban non-slum, and rural areas.

• Individuals who had received 2 doses of COVID-19 vaccine showed significantly higher seroprevalence when compared with unvaccinated individuals.

• Antibodies against SARS-CoV-2 were evident in nearly 85% of healthcare workers working in district-level health facilities.

• As India is identified to have about one-third of the population with no detectable antibodies against SARS-CoV-2 in June–July 2021, acceleration of the coverage of COVID-19 vaccination among adults is recommended.