NEW YORK — More than one in five New Yorkers may have already had the new coronavirus, a testing sample showed Thursday (April 24), suggesting infections are much higher than confirmed cases suggest.

Widespread testing — including for antibodies — is viewed as key to American states being able to lift stay-at-home orders and reopen their shuttered economies.

The presence of antibodies means a person has already been infected with the virus and might mean they are immune, meaning they could likely return to work without catching the illness again.

A total of 3,000 customers at supermarkets across the state of New York were randomly tested for coronavirus antibodies this week, Governor Andrew Cuomo said Thursday.

Almost 14 per cent of them registered positive, he told reporters. In New York City, 21 per cent of tests came back positive.

Those would translate to roughly 2.6 million people statewide and around 1.7 million people in the Big Apple as having already had the new coronavirus.

Those numbers are way above the 263,460 declared cases across New York state, the epicenter of America's outbreak, where the virus has killed more than 15,500 people.

"It's vital for any state, I believe, to first get a baseline study of where you are on the infection rate," Mr Cuomo said.

There are uncertainties about the accuracy of antibody tests and the sample was small. But Mr  Cuomo noted that, if the data played out across the state it would mean that the death rate for Covid-19 there was only 0.5 per cent.

That is much lower than the US average and the worst-affected countries in Europe, which are based on confirmed cases.

According to Johns Hopkins University, Belgium has a known-case mortality rate of 14.9 per cent, France 13.6 percent and the United States 5.5 per cent. AFP