Reinfections, still rare, provide clues on immunity

Scientists are taking a keen interest in people who develop COVID-19 twice. Such reinfections hint immunity against COVID-19 may be fragile and wane relatively quickly, with implications not just for the risks facing recovered patients, but also for how long future vaccines might protect people. Only 25 people so far have been confirmed to be reinfected, but that9s in part because the bar is high: A patient must have had a positive test twice with at least one symptom-free month in between, but there also have to be two full virus sequences, from the first and second illnesses, to rule out that the second test detected nonreplicating viral material or a virus that was suppressed but not fully cleared. Whereas some scientists expect the number of reinfections to go up in the months ahead as early cases begin to lose their immunity, others are more optimistic that an infection with COVID-19 will protect longer lasting immunity.