How it works: When the body is exposed to a virus, the immune system begins to produce antibodies to fight the virus and future infections from it.

Those antibodies stick around after the virus is cleared from the body, making them an indicator of past infection.

Serological tests check the blood for these antibodies — providing confirmation of infection and possible protection.

That’s different from the diagnostic tests receiving most of the public’s attention; those confirm whether someone has an active infection.

These tests could be especially useful for determining whether health care workers have some immunity and are at lower risk if they go back to work, says Nick Evans, an assistant professor at UMass Lowell.