CHENNAI: The fourth phase of sero-surveillance, conducted by the Directorate of Public Health, showed that 87 per cent of people tested in Tamil Nadu have antibodies to Covid-19. The cross-sectional survey was conducted in the last week of December 2021, at the beginning of the third wave driven by the highly-transmissible Omicron variant. In the third phase of the survey, the State’s seropositivity rate was 70 per cent.
The survey results, released by Health Minister Ma Subramanian on Wednesday, show that Tiruvarur district has a seropositivity of 93 per cent, the highest in the State while Chennai’s seropositivity is 88 per cent.
Of the 32,245 people tested as part of 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. Among the 4,921 unvaccinated people tested, 3,374 (69 per cent) had 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 said. It also showed that 68 per cent of unvaccinated people aged 11-18 had detectable levels of antibodies, which is indirect evidence of exposure to natural infection.
Seropositivity rate under 85% in 4 dists
The seropositivity rate was below 85 per cent in only four districts - Tirupathur (82 per cent), Kancheepuram (83 per cent), and Villupuram and Dharmapuri (84 per cent). As part of the survey, samples were taken from people above the age of 10 years from 1,076 clusters across all districts. Each cluster had 30 participants drawn randomly from the locality.
In Phase I of the sero-survey conducted in October/November 2020, the State had a seropositivity rate of 32 per cent. It fell to 29 per cent during Phase II conducted in April 2021, and shot up to 70 per cent in Phase III which was conducted in July/August 2021.
Collectors have been told to increase the vaccination coverage in districts with a seropositivity rate below 84 per cent, Subramanian said. He added the first-dose vaccination coverage in the 15-18 age group is 80.48 per cent, while the second-dose coverage is 22.13 per cent. The 22nd mega vaccination camp will be held on Saturday, and a booster-dose camp on Thursday. The minister added that while in Chennai, only 350 Covid-19 patients are in hospitals, only four per cent of active cases are in hospitals across the State.
‘Guv can’t return the Bill’
Subramanian said there is no chance of Governor RN Ravi again returning the NEET Bill to the Assembly. “He must send it for the President’s assent,” he added.
97% samples are Omicron, just 3% are Delta variant
Whole genome sequencing results obtained on Jan 26 show that 97% of samples were of Omicron variant, and only 3% were of Delta variant. On Dec 7, all samples were of Delta, but by Dec 11, 13% were of Omicron