Serological survey: 22.86% prevalence rate in Capital

New Delhi: The much-awaited results of the Serological survey in Delhi were released on Tuesday, with the National Centre Disease Control announcing that eight of the 11 districts covered in the survey had a prevalence rate of over 20 per cent. The survey concluded that 23.48 per cent of those tested had been exposed to the novel Coronavirus and as a result developed IgG antibodies.

NCDC Director Dr Surjeet Kumar Singh said, "When the prevalence was adjusted against the sensitivity and specificity of the ELISA test kits, the prevalence in Delhi was found to be 22.86 per cent and this is an adjusted figure."

However, NITI Aayog Member, Dr VK Paul pointed out that the survey paints an older picture of the pandemic in the city, precisely because it tests for the presence of antibodies in a subject. He said, "As antibodies take around 14 days to develop, the study represents the picture of Delhi around the third week of June, (18th and 19th day of the month) when the cases were increasing at a high speed."

Director Singh added the remaining 77 per cent of the tested population is still vulnerable to the contagious disease and containment measures need to continue with equal rigour for effective handling of the pandemic.

He attributed this to the government's efforts to prevent the spread of infection, such as lockdown, containment and surveillance measures, including contact tracing and tracking, as well as citizen's compliance to COVID-19 appropriate behaviours.

The study was conducted from June 27 to July 10 by the NCDC after efforts to rein in the pandemic were combined between the Centre, Delhi government and civic bodies. A total of 21,387 samples were tested in the survey, making it one of the largest sero-prevalence studies conducted in the country using the ELISA testing.

The survey also indicated that a large number of infected people remain asymptomatic. "Symptoms-based screening and testing policy may not be able to assess the burden of infection in the community effectively, hence, periodic sero-surveys are required to assess the extent of infection in the community," Director Singh said.

Southeast district was found to have sero-prevalence of 22.12 per cent, Shahdara 27.61 per cent, northwest 23.31 per cent, New Delhi 22.87 per cent, central 27.86 per cent, southwest 12.95 per cent, northeast 27.7 per cent, east 23.9 per cent, north 25.26 per cent, south 18.61 per cent and west 19.13 per cent.

Meanwhile, experts in the city have said that the findings of the sero-survey show that Delhi is far from attaining herd immunity and that people must not let their guard down. Anurag Agarwal, the director of the Institute of Genomics and Integrative Biology, said the findings indicate that around 25 per cent people have recovered from the disease, after adjusting for sensitivity and specificity.

"Since some people may not have developed adequate antibodies, the actual number may be as high as 30 per cent. This suggests that interaction pairs capable of disease transmission amongst Delhi residents will be fewer and the transmission chains shorter," he added.

Further, the Delhi government has said, "We will consult public health experts and epidemiologists to determine if the future course of Delhi's strategy against COVID-19 should change in light of these survey results or not," the official also said.