Tamil Nadu has an overall seroprevalence — which is the presence of antibodies to SARS-CoV-2 — of 66.2%. Among the 38 districts, Virudhunagar had the highest seropositivity at 84%, while Erode had the lowest at 37%, according to the Directorate of Public Health (DPH) and Preventive Medicine’s phase-III cross-sectional serosurvey conducted in July.
The State’s seroprevalence was 29% during the second survey conducted in April 2021 and 31% during October-November 2020. Of the 26,610 samples tested from 888 clusters for the third round of the serosurvey, 17,624 individuals had IgG antibodies against SARS-CoV-2.
In fact, the Indian Council of Medical Research’s national survey that covered three districts in TN during June-July put the State’s seropositivity at 67.6%.
According to the DPH report, the overall seropositivity of 66.2% could be attributed to the timing of the serosurvey and vaccination coverage. The phase III serosurvey was conducted during the declining phase of COVID-19’s second wave in the State.
Intense vaccination drives conducted from January 16 and the inclusion of 18+ age individuals for vaccination would have generated protective antibodies in the population. As of June 10, 97.6 lakh persons got vaccinated — either single or double dose — in the State, it said.
Western districts such as Erode, Coimbatore and Tiruppur have reported around 45% seropositivity which could be attributed to the consistent reporting of new COVID-19 cases in these regions, the report added.
Among the 38 districts, seroprevalence was more than 50% in 33 districts unlike in the previous two surveys in which seropositivity remained under 50%. After Virudhunagar, Chennai had the highest seropositivity at 82% as against 49% in the previous round. As many as 11 districts had seropositivity in the range of 70 to 79%. These include Madurai (79%), Tenkasi (78%), Theni (77%), Tirunelveli (76%) and Ramanathapuram (75%).
After Erode, Coimbatore had the least seroprevalence at 43%. Tiruppur’s seropositivity stood at 46%, while Nagapattinam and Namakkal had 47% and 48% seropositivity respectively.
