Data out of South Korea has put a question mark on the supposed immunity afforded patients who've recovered from the coronavirus. According to South Korea's Centers for Disease Control and Prevention, 51 recovered patients returned positive tests within days of leaving quarantine in the city of Daegu—"the epicenter of the outbreak" in the country, per the Sun. According to experts, the short duration between tests suggests the patients didn't encounter the virus for a second time, but they can't be sure. "While we are putting more weight on reactivation as the possible cause, we are conducting a comprehensive study on this," says Jeong Eun-kyeong, the center's director, per Bloomberg. The outlet reports patients in China considered to have recovered have also tested positive again and some have gone on to die, raising similar fears about reinfection.
That may not be the case, though. Patients are considered recovered after two negative tests within 24 hours, but "there have been many cases when a patient during treatment will test negative one day and positive another," Jeong says. That could mean there are false negatives happening, with the virus hiding imperceptibly in the body, per Slate. The Verge also notes the cotton swab test for the virus reaches into a hard-to-reach part of the body—the nasopharynx, where the back of the nose meets the throat. If the test isn't done correctly, it can turn up an erroneous result. The health authority is working to gain more information. In the meantime, Penn Medicine and the Mayo Clinic are developing tests to detect prior virus exposure, which may result in no symptoms. Health care workers are intended as the first recipients of the tests, which look for antibodies in blood, per Business Insider. (Read more coronavirus stories.)