Sero-prevalance survey in Tamil Nadu shows 70% people have antibodies against Covid-19

The third survey was conducted in July and August just after the second wave of infections began to decline and shows that 70% of the population have IgG antibodies against the Covid-19 infection.

Tamil Nadu’s third survey shows a sero-prevalence of 70% across the state with the districts of Virudhunagar, Tenkasi and Chennai being the highest at 88%, 83% and 82% respectively. In the surveys done earlier, the state showed a sero-prevalence of 32% in October-November last year and 29% this April.

Coimbatore, Erode and Salem, in the western region of Tamil Nadu which had fewer infections during the first wave but were severely affected during the second wave showed a sero-positivity of 71%, 70% and 60% respectively. The lowest sero-prevalence was found in Karur district with 51%. (PTI PHOTO.)

The third survey was conducted in July and August just after the second wave of infections began to decline and shows that 70% of the population have IgG antibodies against the Covid-19 infection. According to the survey conducted by the Directorate of Public Health and Preventive Medicine, blood samples were drawn from 24,586 people from 827 clusters to be tested using Chemiluminescence based Immuno Assay (CLIA). Each cluster consisted of 30 participants drawn randomly from a village in a rural area or a street in the case of urban regions. Nearly 17,090 people were found to have the presence of IgG antibodies against the SARS CoV-2 virus.

Coimbatore, Erode and Salem, in the western region of Tamil Nadu which had fewer infections during the first wave but were severely affected during the second wave showed a sero-positivity of 71%, 70% and 60% respectively. The lowest sero-prevalence was found in Karur district with 51%.

The health department says that this is a re-survey as the findings were first released on July 31 which showed a sero prevalence of 66.2%. “We conducted the third survey in July from which we took two extremes--the highest positivity in five districts and the lowest positivity in five districts-- and we re-did the survey in these 10 districts to check if there are any variations but it’s almost the same,” said director of DPH, Dr V S Selvavinayagam.

“However, the re-survey confirms our findings and the ground situation so we have now released the combined results of July to August,” he said. This comes at a time when Covid-19 infections have declined and there is an increase in vaccinations. “It’s a reflection of the vaccination status. 70% positivity is good but we need to go beyond this,” he added.