E-Paper
Tamil Nadu's seroprevalence down from 31% in first Covid-19 wave to 23% in April
The study was carried out by the Directorate of Public Health and Preventive Medicine across all districts except Chennai.
(The second serosurvey was conducted in Tamil Nadu in April this year which showed that 23% of people had SARS-CoV-2 antibodies which is a decline from the first survey which showed 31% in October-November last year.
“The first survey was initiated around four weeks following the peak cases reported in August 2020 during the first wave,” the report stated, adding that this time it was conducted close to the beginning of the second wave.
“Waning of IgG antibodies during the time gap of five months between 1st and 2nd survey (November 2020 to March 2021) could be one of the valid reasons for low seroprevalence as reported by several studies published in international journals,” it said.
The study was carried out by the Directorate of Public Health and Preventive Medicine across all districts except Chennai. Out of 22,904 samples that were tested, 5,316 people had IgG antibodies against the novel coronavirus disease. The report also said various coronavirus variants, including the B.1.617.2 (Delta) of Indian origin, were detected in Tamil Nadu.
The highest seropositivity was found in the Tiruvallur district at 49% and the lowest in Nagapattinam at 9%. About 756 clusters were picked and each cluster consisted of roughly 30 participants who were randomly picked from a village, rural areas, a street and an urban area.
A similar survey was conducted for the first time. About 22,690 blood samples were drawn and 6,995 were found reactive to the antibodies. The report attributed the "sharp decline" from 31% last year to 23% now in the second survey to four factors - the timing of the serosurvey, waning of antibodies, vaccination coverage and the emergence of SARS CoV-2 variants.
A third serosurvey is being planned for July-August. The department said it would be an appropriate time considering the current decline trend of Covid-19 cases combined with increased vaccinations for those above 18 years of age.
