Chennai, Feb 10 (IANS): The fourth phase of the Sero surveillance study conducted by the Tamil Nadu health department has revealed that around 87 per cent of people tested in the state have antibodies to Covid. The cross-sectional survey was conducted in December 2021 at the beginning of the Omicron variant triggered the third wave.

It may be noted that in the third phase of the sero-surveillance survey, 70 per cent of the people tested had antibodies.

The state health minister Ma Subramanian in a statement on Wednesday said that Tiruvarur district had the highest seropositivity rate of 93 per cent in the state. The seropositivity of Chennai was 88 per cent, according to the minister. The statement said that in four districts of the state seropositivity rate was below 85 per cent. Tirupathur (82 per cent), Kancheepuram (83 per cent), Villupuram and Dharmapuri (84 per cent).

Of the 32,245 people tested for the survey, 27,324 (85 per cent) were vaccinated and among them, 24,667 (90 per cent ) had detectable levels of anti-SARS-CoV-2 IgG antibodies.

Interestingly, the statement said that of the 4,921 unvaccinated people tested as part of the study, 3374 (69 per cent) had developed antibodies.

The study highlighted that vaccinated people have better detectable antibody levels. Among those who took Covaxin or Covishield, more than 80 per cent had antibodies. The study also found that 68 per cent of unvaccinated people aged 11-18 had detectable levels of antibodies. The health department said that this was evidence of indirect exposure to natural infection.

Tamil Nadu health minister Ma Subramanian while speaking to IANS said, "The state public health department has taken samples from people above the age of 10 years from 1,076 clusters across all districts of the state and found that at an average 87 per cent have developed antibodies and this is a good sign."

He said that each cluster had 30 persons drawn randomly from the community and said that district collectors were told to increase the vaccination coverage in districts with a seropositivity rate below 84 per cent. Thirupathur with 82 per cent, Kancheepuram with 83 per cent, and Villupuram and Dharmapuri with 84 per cent fall under this category, the minister said.

Meanwhile, the whole genome sequencing conducted on January 26 found that 97 per cent of samples were the Omicron variant while only 3 per cent was the Delta variant of the Covid-19 virus.

Interestingly on December 7, all samples were Delta, but on December 11, 87 per cent were Delta while 13 per cent of the Omicron variant.

The Tamil Nadu health minister said that the first dose vaccination coverage for children in the age group of 15-18 is 80.48 per cent while the second dose coverage is 22.13 per cent. He also said that only four per cent of the active cases are admitted in hospitals across the state.