Nearly 15% of India’s population may have developed antibodies against Covid-19, according to an analysis by a private laboratory. Thyrocare, a private diagnostic laboratory, on Tuesday shared the data from its 60,000 antibody tests conducted across 600 locations over 20 days.
According to Thyrocare’s data, the highest positivity rate for the antibody test is in Bhiwandi, Thane, at 47.1%. The lowest positivity rate was found to be in Alibag in Maharashtra at 0.7%. In Mumbai, Thyrocare tested 5,485 people and found antibodies in 1,501 (27.3%).
Thyrocare is one of the few private laboratories listed by the government to conduct antibody tests. The laboratory used Elisa (enzyme-linked immunosorbent assay) and Chemiluminescence immunoassay (CLIA) antibody tests to arrive at the findings. The Pune-based National Institute of Virology, which came up with the Elisa test for Covid-19, claims it has high sensitivity and specificity, reported Times Now. An antibody test is only used as a surveillance tool, and not for diagnosis, to assess the level of exposure.
Thyrocare Managing Director and Chief Executive Officer A Velumani, had said on July 17 that 180 million Indians may have been already silently immunised in India. “Too good to believe,” he had tweeted. “Hope kits do not have high false positives.”
The findings came on the same day the government released the results of an antibody testing survey in Delhi. It showed that 23.48% of the participants developed Immunoglobulin G antibodies that indicate they may have been infected by the coronavirus. The study also noted that a large number of those infected were asymptomatic.
Cannot generalise findings
However, experts said the findings of Thyrocare cannot be generalised. “It’s good that a private laboratory has conducted as many as 60,000 antibody tests,” Amit Singh, associate professor at the Centre for Infectious Disease Research, IISc, in Bengaluru told Hindustan Times.
“ICMR [Indian Council of Medical Research] had conducted around 20,000. However, the numbers are too low to generalise. I don’t know if most representative areas are covered and population heterogeneity is also a factor. From the list of areas it appears that the focus has been urban or semi-urban areas. We cannot generalise the findings for rural areas,” Singh said.
“The antibody positivity rate shows a larger population has been infected and didn’t realise because no symptoms emerged,” said Dr Caesar Sen Gupta, head of operations at Thyrocare, told The Indian Express. Velumani said he hoped to get a clearer picture by July 30 by which the laboratory is likely to conduct 1.2 lakh tests.