NEW YORK — More evidence is emerging that far more New Yorkers have had the coronavirus than the number confirmed by lab tests, officials said Thursday, offering insight that could help authorities decide how and how quickly to let people stop isolating from friends and return to work.

Blood samples collected from about 3,000 people indicated that nearly 14 percent had developed antibodies to fight a coronavirus infection, Gov. Andrew Cuomo said at his daily news briefing.

In New York City, the epicenter of the pandemic in the U.S., 21 percent of the people tested had antibodies.

It’s not know yet how much protection antibodies provide or how long that immunity might last, and Cuomo cautioned that the data was preliminary. The sample of people tested was small. Participants were hastily recruited at shopping centers and grocery stores, meaning they were healthy enough to be out in public.

But the governor said knowing how many people have antibodies — and who might possibly be immune to the virus — could potentially help set policy on when to reopen parts of the state.

“We’ll have a larger and larger sample. But I want to see snapshots of what is happening with that rate. Is it going up, is it flat, is it down? And it can really give us data to make decisions,” Cuomo said.

Earlier Thursday, New York City’s health commissioner said as many as 1 million people in New York City may have been exposed to the coronavirus.

Across the country, scientists are rolling out blood tests that look for antibodies, proteins that the immune system makes to fight off infection. They don’t detect active infection like the tests for the currently sick. They’re intended to tell who had previously been infected whether they knew it or not.

The New York study is the latest in a small wave of early attempts to try to better determine how widespread infections have been in certain geographic areas. A study in Santa Clara County, California, put the figure at somewhere around 3 percent to 4 percent. Another California study, in Los Angeles County, came up with roughly the same percentage.