Knowledge of population-level immunity is critical for understanding the epidemiology of SARS-CoV-2 (COVID-19) and formulating an infection control policy, including both non-pharmaceutical interventions and vaccination campaigns. To facilitate this policymaking, the state government of Tamil Nadu, conducted population-level serological surveys four times, in October–November 2020, April 2021, June–July 2021, and December 2021–January 2022 (shaded sections of Fig. 1). In each round, the survey was conducted on representative populations in every district of the state, except Chennai in round 2. Tamil Nadu is the 6th most populous state in India, with roughly 72 million persons. India, including Tamil Nadu, experienced three COVID-19
waves that peaked in September 2020, May 2021, and February 2022. Moreover, each state in India began a vaccination campaign in January 2021. Roughly half the population, 714 million persons, were vaccinated by February 1, 2022. Thus, the state’s four serological surveys span the period between the end of the first wave and the start of the third wave and mid-point of the country’s first vaccination campaign.
This paper was published in the journal, Nature Scientific Reports.
