Knowing who has had COVID-19 and who likely immune to catching it again has many benefits. "If [a person] have a robust response, then you know that they're likely to be immune [to the virus]. They could be the person who goes out for groceries every week, who checks the mail and does everything critical," says Dr. Nessari. "They also could be the early people to return to somewhat normal activity. More importantly, they could be identified as potential donors for plasma for people who have severe COVID-19."