Mayo Clinic and the U-of-M are reportedly close to having antibody tests which could determine if someone has already been infected with COVID-19 without knowing it, and has recovered. Governor Tim Walz says:

“Certainly that gives us the ability of who wouldn’t need to be quarantined, who could be out and is not infecting others while (they) themselves are healthy, and I think that’s where some potential lies.”

But what’s unknown at this point: If some people have natural immunity to COVID-19… and whether a person can be re-infected once they’ve had the disease.