For governments hoping to reopen their economies, antibody tests are usually seen as a key tool to do so. They can confirm if a person has had the virus but was asymptomatic, helping to understand the actual scale of the outbreak.

New York Governor Andrew Cuomo took an important a step in support of this approach, announcing the state will begin a massive antibody testing campaign to get a grasp on the number of people who have been infected with the coronavirus.

Antibody tests (also called serological tests) differ from diagnosis tests in a key aspect. Whereas the diagnosis tests show who has the virus now, antibody tests show who has had it in the past and has developed an immune response. Since many cases are asymptomatic, antibody tests are crucial in determining how far the disease has actually spread, and who is “safe” to return into society.

Cuomo said the state will carry out an initial 2,000 antibody tests per day, or 14,000 a week, on a random group of citizens, in addition to the diagnostic testing for the virus. It will be the “largest survey of any state population that has been done,” according to Cuomo.

“We’ll take thousands of tests, antibody tests, over this next week all across the state to give us a real snapshot, a real baseline, of exactly how many people were infected by coronavirus and have the antibodies,” Cuomo said. “So we’ll have the first real statistical number on exactly where we are as a population.”

More than 617,000 New Yorkers have been tested for COVID-19 so far, 242,786 of whom were positive for the virus, state health officials reported. Nearly 14,000 people have died from COVID-19 in the state.

The antibody tests were approved by the US Food and Drug Administration (FDA) and will give the state its “first true snapshot” of how many people in the state have been infected with COVID-19, Cuomo said.

“We don’t really know how many people were infected. How many people had coronavirus but self-resolved? We don’t really know because we haven’t been able to do testing on that large of scale,” Cuomo said. “We’re going to do that in the most aggressive way in the nation.”

The governor asked the federal government to work with New York and other states to address all the logistical and supply chain problems that alter the capacity to do a larger number of tests. He also called for the Trump administration to pass legislation to help states respond to the pandemic.

“The states must do their part and the federal government must do its part,” Cuomo said when asked about President Donald Trump’s Twitter assertion that his administration will support governors, but they “must be able to step up and get the job done” on testing. “Perfect, that’s called partnership, I agree,” Cuomo said.

While the antibody tests could be helpful as mentioned by Cuomo, their actual usefulness depends on the supposition that those who have had the virus are immune to new infections, an argument that is still an open question. Earlier reports of reinfection have been seen in China and in Japan, and notably, the UK’s attempts to mass-test its population were marred by tests that didn’t truly work.

The decision to carry out an antibody test campaign comes a few days after Cuomo signed an order asking all New Yorkers must have a mask or mouth and nose covering when they are not maintaining social distancing in public. This includes using the subway or walking on a busy street.