More than 63 million people in India may have contracted coronavirus (Covid-19), health authorities said on Tuesday -- about 10 times higher than the official reported figures.
According to a survey of the Indian Council of Medical Research, about one in 15 people above the age of 10 had antibodies against the virus.
The survey was conducted from mid-August to mid-September, according to global media reports.
Antibody tests, also known as serology tests, check for proteins called antibodies in the immune system, which indicate if someone has been exposed to the virus.
Of the country's 1.3 billion citizens, more than 966 million are aged 10 or above, according to the government's most recent census in 2011.
If one in 15 people of this group have been infected with the virus, that is a total of 63.78 million people.
As of Wednesday, India has reported more than 6.1 million cases and 96,000 deaths, according to data compiled by Johns Hopkins University.
The survey suggests that for every one infection officially reported, there are actually 26 to 32 people infected who slip through the cracks, said Dr. Balram Bhargava, director of the medical council, at a news conference on Tuesday.
This falls in line with what many experts have warned for months -- that India's coronavirus crisis may be much more dire than official figures suggest.
There are numerous reasons for this: People simply aren't getting tested enough. There are sometimes errors in reporting and registering cases. Changing government strategies can muddle the numbers and paint a misleading picture of the situation.
The government began rolling back restrictions in May after a months-long lockdown, with ministers turning their attention to reopening the economy and public services. But experts, including Bhargava, warn that it's too soon to relax.
"Since a large proportion of the population is still susceptible, prevention fatigue has to be avoided," Bhargava said, adding that the risk of infection was highest in urban slums where millions live in crowded conditions, often with limited sanitation or running water.
Slum residents had a seroprevalence -- meaning they carried antibodies -- of 15.6 per cent, almost double the 8.2 per cent detected in residents of non-slum urban areas.
The figure drops in rural areas to 4.4 per cent, according to the survey.