After screening 24,586 people from across the state, the directorate found that nearly 70% (17,090) had antibodies against the virus. In the first state-wide serosurvey done in October-November 2020, before the second wave, the positivity rate was around 32%. This went down to 29% during the second sero survey in April 2021. Several districts reported a drop in positivity rate as cases went down between September 2020 and March 2021.
But after the second wave that began in April, there has been a sharp increase in seropositivity rate. Public health officials say these antibodies were acquired either thorough infection or immunization, said director of public health Dr TS Selvavinayagam. The highest antibody rate was observed in Virudhunagar (84) and Tenkasi (83%). While Chennai reported 82% positivity rate, Coimbatore logged 71% and Madurai had 79%. Karur had the lowest seropositivity rate at 51%. Perambalur (58%), Ariyalur(56%) and Nilgiris (55%) also had seropositivity rate below 60%.
Health minister Ma Subramanian, who released the sero results on Thursday, said the state will focus on vaccinating 100% of the population in districts where seropositivity is lower than 60%. “We want all the elderly and vulnerable population to take two doses of the vaccine. This is the only way we can prevent hospitalization and death due to the virus,” he said.