The phase 3 of state-wide cross sectional serosurvey done in July by the Directorate of Public Health and Preventive Medicine done surveyed 26,610 people from 888 clusters across districts.

from Times of India https://timesofindia.indiatimes.com/city/chennai/serosurvey-finds-covid-antibodies-in-66-2-of-tamil-nadu-people-its-82-in-chennaiites/articleshow/84923223.cms