Serological tests identify the antibodies a patient’s body produces when it fights this strain of the coronavirus. They test for past infections, not current ones.

Some people likely contracted the coronavirus but didn’t feel sick, or weren’t able to get a diagnostic test. Serology tests will confirm whether they had it. And on a larger scale that will provide more information about where the virus spread, the real number of cases and the actual death rate from the virus.

Yes, but: “People just think this is the solution, that this is finally the thing, that everybody is going to have immunity passports … and I am very skeptical of this for a variety of reasons,” said Ashish Jha, professor of global health at the Harvard T.H. Chan School of Public Health.

“It’s going to have limited utility outside of hotspot cities and outside of professions where you’re going to see higher exposure,” former Food and Drug Administration Commissioner Scott Gottlieb told me.