Some coronavirus patients 'cured' in South Korea tested positive again

The notion of coronavirus immunity is still in question after an announcement from South Korea's CDC.

In a Monday briefing, South Korea's Centers for Disease Control and Prevention announced 51 people "cured" after contracting COVID-19 had tested positive for the disease after being released from quarantine. CDC Director Jeong Eun-kyeong leaned toward deeming these cases a "reactivation" of the virus, but will study it further.

While it was never certain, the idea that people who test positive for and then recover from the new coronavirus gain immunity from the disease had even informed government policy in some countries. The U.K. originally resisted closing down businesses and enforcing social distancing guidelines in an effort to spread "herd immunity" among its citizens, for one.

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But this latest announcement calls the herd immunity strategy into further question. Patients are deemed recovered when they test negative for the disease twice in 24 hours. Yet in at least 51 cases, people who had apparently recovered had tested positive again shortly after they left quarantine. "While we are putting more weight on reactivation as the possible cause, we are conducting a comprehensive study on this," Jeong said. Those patients may not have even been cured at all, seeing as "there have been many cases when a patient during treatment will test negative one day and positive another," he said.