CHENNAI: About one-third of Chennai’s population may have been exposed to Covid-19, data from a recent seroprevalence survey, conducted by the city corporation, suggested. However, the Corporation has neither shared details of the methodology adopted in the survey, nor a break-up of zone-wise data. In this context, health secretary Dr J Radhakrishnan cautioned that any extrapolation based on the data might not reflect the actual situation.
The survey was conducted in October to identify the presence of Immunoglobulin G (IgG) antibodies in a given population. As antibodies develop in response to an infection, such as Covid-19, their presence suggests exposure to the Coronavirus. As part of the survey, samples of 6,389 people were tested. Of that, samples of 2,062 -- or 32.3 per cent -- showed a presence of antibodies, indicating exposure to the virus.
In comparison, the results from the Corporation’s first sero-survey, conducted in July, indicated that about one-fifth or 16.6 per cent of the Chennai population had been exposed to the virus. In the first survey, 12,405 individuals were tested, and the samples of 2,673 showed a presence of antibodies.
The first survey also showed drastic variations from zone to zone with about 44 per cent showing exposure in Tondiarpet, in which several clusters were initially reported, while only seven per cent of samples in Madhavaram zone were positive for antibodies.
Speaking to The New Indian Express, Radhakrishnan warned that sero surveys were used for only surveillance and needed to be interpreted by disaggregated data.
“Unless we get zone-wise data, extrapolation based on these results will not be a proper reflection (of the situation) and might make people complacent,” he said.
“I am sure the Corporation will share the details of where the samples were taken and methodology adopted in conducting the survey,” added Dr Radhakrishnan.
However, when Express tried to contact Deputy Commissioner of Health, Madhusudanan Reddy, to understand the methodology adopted by the Corporation for the survey, the official could not be reached.
Meanwhile, based on the results shared by the Corporation, renowned virologist Dr Jacob John posited that as the Covid-19 exposure seemed to be significantly high, there may not be another wave of infection in the city.
“If the survey shows 30 per cent of the population were exposed to the virus, the actual proportion of people exposed might be.
Therefore, I don’t expect a second wave,” he said, although he added that there could be a spike in cases in busy areas such as Koyambedu.
Dr Prabhdeep Kaur, Deputy Director, Indian Council of Medical Research–National Institute of Epidemiology disagreed.
“(Going by the results) still nearly 70 per cent of the population is susceptible,” she said. She also pointed out that it is still unknown how long the effect of natural immunity to the virus might last.