A re-survey of the third serosurvey has put Tamil Nadu’s overall seroprevalence at 70%. Of the 37 districts, Virudhunagar, Tenkasi and Chennai have over 80% seropositivity, while Perambalur, Ariyalur, the Nilgiris and Karur have seropositivity of less than 60%.
The Directorate of Public Health and Preventive Medicine had taken up the State-wide Cross Sectional Serosurvey-Phase III during July-August 2021. A total of 827 clusters were included, with 24,586 samples covered. Among them, 17,090 individuals had IgG antibodies against SARS-CoV-2, the virus that is causing COVID-19. The findings that were first released on July 31 put the overall seroprevalence — the presence of antibodies to SARS-CoV-2 — at 66.2%.
On Thursday, the Directorate released the findings of a re-survey. “Five districts in each upper/lower limit are resurveyed as a measure of reconfirmation. Our results are in confirmation with the latest Indian Council of Medical Research survey,” said T. S. Selvavinayagam, Director of Public Health and Preventive Medicine.
The seropositivity of Virudhunagar, which remained on top of the chart, rose from 84% to 88% following the re-survey. Tenkasi came in second with a seroprevalence of 83%, which was previously 78%. Chennai’s seropositivity remained unchanged at 82%. Madurai and Theni had a seropositivity of 79% and 76% respectively.
In fact, the seroprevalence went up in some western districts that previously had the lowest levels. The seropositivity of Erode, which earlier found itself at the bottom of the table with 37%, rose to 70%, while Coimbatore had 71% (previously 43%) and Tiruppur had 70% (previously 46%). Officials attributed the increase to the exposure to infection and the ramping up of vaccination.
Four districts reported a seropositivity of less than 60% — Perambalur (58%), Ariyalur (56%), the Nilgiris (55%) and Karur (51%).
“We are moving towards a safer zone. The ongoing rapid vaccination through mega camps is helping us in moving fast,” Dr. Selvavinayagam said. Earlier, the State-wide serosurveys conducted by the Directorate found a seropositivity of 32% during October/November 2020 and 29% in April 2021.
