Antibody tests on a random sample of people suggest nearly one in four residents in India's capital, Delhi, has been exposed to coronavirus infection.
Antibody tests check your blood by looking for antibodies, which may tell you if you had a past infection with the virus that causes COVID-19. The government survey said 23.48% of the 21,387 people whose blood samples were tested had Covid-19 antibodies.
It suggests that infections in the city are much more widespread than the number of confirmed cases indicates.
Delhi has so far recorded 123,747 cases, equivalent to less than 1% of its population of 19.8 million.
At 23.44%, the number of infections would be 4.65 million in a city that size.
A government press release says the difference shows that "a large number of infected persons remain asymptomatic".
It even says the figure of 23.48% may be too low because Delhi has several pockets of dense population.
But it adds that "a significant proportion of the population is still vulnerable" and all safety measures must be strictly followed.
Experts say the study, the first of its kind in India, is crucial because it will help authorities understand the spread of the virus better.
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