TN Serosurvey finds COVID antibodies in 66 per cent population

The third Tamil Nadu Cross Sectional Serosurvey in July, covering over 26,000 samples revealed that at least 66.2 per cent of the population has developed antibodies to SARS-CoV-2, the virus which causes covid-19.

Among the 26,610 samples tested, 17,624 individuals had IgG (Immunoglobulin G) antibodies against SARS-CoV-2 virus.

While the overall seroprevalence was 66.2 percent, the highest seropositivity was observed in Virudhunagar district at 84 per cent while Erode in west Tamil Nadu reported the lowest at 37, according to the latest serosuvrey conducted by the Directorate of Public Health and Preventive Medicine in 888 clusters across the state.

It was released by state Minister for Medical and Family Welfare Ma Subramanian in the presence of Principal Health Secretary Dr J Radhakrishnan and Director of Public Health (DPH) and Preventive Medicine Dr T S Selvavinayagam, here on Saturday.

In the earlier state-wide serosurveys conducted by DPH&PM, the seropositivity was 31 percent in October/ November 2020, and 29 percent (in the second conducted in April 2021).

The overall seropositivity of 66.2 percent detected during the third survey could be attributed to various possible reasons including the timing of serosurvey conducted during the declining phase of the covid second wave in Tamil Nadu, it said.

"Intense vaccination drives across the state from January 16, 2021 and inclusion of 18+ age individuals for vaccination would have generated protective antibodies in the population. As on June 10, 2021, 97.6 lakh people got vaccinated (either single or double dose) in Tamil Nadu," the survey report said.

Western districts like Erode, Coimbatore and Tiruppur reported around 45 percent seropositivity which could be attributed to the consistent reporting of new covid-19 cases in these regions, it said.

The serosurvey was successfully completed under the supervision of Selvavinayagam and his team at the state and district level.

Each cluster consisted of 30 participants drawn randomly from a village in a rural area or a street in the case of an urban one.

Blood samples were collected from a total of 26,610 participants and tested for the presence of SARS CoV-2 IgG antibodies using Chemiluminescence based Immuno Assay (CLIA).

All the samples were tested at six referral labs of DPH & PM located in Chennai, Tiruchirappalli, Madurai, Coimbatore, Tirunelveli and Salem for the detection of IgG antibodies.

On Friday, Tamil Nadu reported 1,947 new covid-19 cases taking the overall tally to 25,57,611.

With 27 deaths due to the infection, the toll rose to 34,050.

Over 2.15 crore persons have taken the jabs through government-run and private hospitals in the state, so far.