Antibodies could indicate whether a person was infected by the virus and recovered — and therefore could potentially reenter public life.

The Centers for Disease Control and Prevention (CDC) has begun conducting blood tests it says will help determine if a person has been exposed to the coronavirus, even without showing symptoms, a CDC spokesperson told Politico.

These serological tests, or sero-surveys, are different from the nose swabs used to diagnose active cases of Covid-19. By analyzing blood, researchers will be able to tell if a person developed certain antibodies in the blood, indicating that they were infected by the virus and recovered.

If a person can be shown to have developed those protections against reinfection, they could potentially reenter society — and the workforce — during a time when millions of Americans live under orders to stay home to prevent the spread of Covid-19.

These tests can also help to retroactively collect data about how widespread the virus has been. In the absence of readily available diagnostic testing, many people who have demonstrated symptoms have simply been told to stay home, without receiving a formal diagnosis, while many more people never display symptoms at all...

The CDC has begun testing blood for immunity against the coronavirus - Vox