Tamil Nadu has an overall seropositivity of 87% as per the phase-IV serosurvey conducted during the last week of December 2021. All 38 districts had a seroprevalence of over 80%, with Tiruvarur topping the list with 93% seropositivity.
The cross-sectional survey for SARS-CoV-2 infection transmission, which was taken up by the Directorate of Public Health and Preventive Medicine prior to the beginning of the Omicron-driven third wave in the country, covered 32,245 individuals aged above 10 years in 1,076 clusters across the State.
According to the findings released by the Directorate on Wednesday, of the 32,245 samples tested for SARS-CoV-2 IgG antibodies, 28,071 individuals had a protective level of antibodies against SARS-CoV-2, indicating an overall seropositivity of 87%. The previous serosurvey conducted during July/August 2021 had observed a seroprevalence of 70%.
A total of 88% of adults included in the phase-IV survey were seropositive and had a protective level of antibodies. One of the salient findings of the serosurvey was that 68% of individuals aged between 11 and 18 years, who were unvaccinated at the time of survey, also had detectable levels of IgG antibodies against SARS-CoV-2, indirect evidence of their exposure to natural infection.
Of the 32,245 participants, 27,324 (85%) were vaccinated. Among them 90% (24,667) had detectable levels of anti-SARS-CoV-2 IgG antibodies. Among the 4,921 unvaccinated persons, 3,374 (69%) had anti-SARS-CoV-2 IgG antibodies, the Directorate said.
The Directorate noted that it was clear that vaccinated individuals have better detectable levels of the antibodies when compared to the non-vaccinated population. Among the 27,324 vaccinated individuals, more than 80% seropositivity was observed in individuals who had taken either Covaxin or Covishield vaccines.
Age-wise distribution of seropositivity
The survey found seropositivity of 68.4% in the age group of 10 to 18 years. In the 18 to 44 years category, 89.5% of individuals were seropositive, while it was 88.6% among the 45 to 59 years group.
Seropositivity of 84.5% was observed in the above 60 years age group.
District-wise seropositivity
With Tiruvarur having the highest seropositivity of 93%, Tenkasi followed with 92%, while five districts -- Kanyakumari, Madurai, Perambalur, Sivagangai and Virudhunagar had 91% seropositivity each. Both Cuddalore and Nagapattinam had a seropositivity of 90%. Chennai’s seropositivity stood at 88%.
Tirupattur had the lowest seroprevalence of 82%. Dharmapuri and Kancheepuram had 83% seroprevalence each.
“While the seroprevalence is reflective of the vaccinations, the seroprevalence among children and among the vaccinated is indicative of the fact that they were exposed to COVID-19. It has also helped in allowing gradual focus on districts which are lower than the State average,” Health Secretary J. Radhakrishnan said.
He added that while the daily media bulletins focus on total numbers and also daily figures behind the scenes, the State has a 360-degree approach in which it uses 331 labs for RT-PCR tests, followed by tracing and medical management, continuing its emphasis on non-medical approach for sustainable control and prevention by taking efforts to create awareness on COVID-19 appropriate behaviour and following up of SOPs for permitted activities. It now focuses on the need to change behaviour on a permanent basis to overcome current and future waves.
“We are also focussing on vaccination of the remaining eligible persons for the first dose and those due/overdue for second dose, coverage of 15-18 years for first and second doses and a drive for booster doses for the elderly with comorbidities, healthcare and frontline workers,” the Health Secretary said.
T.S. Selvavinayagam, Director of Public Health, said, “Purely based on the scientific evidence available as of now, we can hope that we can go back to normal life soon, along with the co-existence of COVID-19. The 87% reactivity in the serosurvey indicates that we have sufficient protective levels of antibodies and 90% coverage with at least one dose of vaccination.”
