An antibody test for the coronavirus can indicate whether someone has been infected, but it’s just one measure of immunity, researchers say. How robust that immunity is and how long it lasts are still open questions.

A paramedic holds a test tube containing a blood sample at a coronavirus antibody testing program at the Hollymore Ambulance Hub, in Birmingham, England, on Friday, June 5, 2020. Making antibody tests widely available may help Britain lift its lockdown restrictions, because they show who has already had the COVID-19 and might have a degree of immunity from coronavirus. (Simon Dawson/Pool via AP)