There is apprehension in South Korea after over 100 persons who had coronavirus and were treated tested positive again.
At least 116 people cleared of the virus have tested positive again, raising questions for authorities.
The number of such relapse cases more than doubled from 51 reported last week, even as officials suggested they would soon look at easing strict recommendations aimed at preventing new outbreaks.
South Korea reported only 25 new cases of the coronavirus overall on Monday, continuing a weeks-long decline. To date, the country has reported a total of 10,537 cases and 217 deaths.
Officials are still investigating the cause of the relapses, but Jeong Eun-kyeong, director of the Korea Centers for Disease Control and Prevention (KCDC), said the virus may have been reactivated, rather than the patients being reinfected.
Other experts said faulty tests may be playing a role, or remnants of the virus may still be in patients' systems.
Reporting from the capital Seoul, Al Jazeera's Rob McBride said the developments were "worrying" for officials worldwide trying to understand the virus.
"Does that mean that there had been a problem in testing? Does it mean that there are many more questions about this virus that the experts simply don’t know? Could it be mutating in some form?" said McBride.
"So there are questions and of course they're questions that are important not only here in South Korea but with epidemiologists the world over, who are in the thick of it as the pandemic advances," he said.
Possible false positives
Archie Clements, professor of infectious disease epidemiology at the Curtin University in Perth, Australia, told Al Jazeera the growing number of those testing positive again in South Korea may simply be because "no diagnostic test is perfect for any disease" and false positives are a fact of testing a large population, especially during the outbreak of a new virus.
Clements also said it is possible the virus is reactivating in the apparently recovered, but noted it was unlikely that those who had previously tested positive and were later cleared had independently picked up the virus a second time.
"I think what is very, very unlikely is that these people are being reinfected by other people," said Clements. "There’s plenty of evidence to suggest that there is quite a strong immune response to infection with coronavirus, and that should protect people from infection for a period of time. What's not currently known is for how long."
South Korea, which has been hailed for its speedy and widespread testing, plans to send 600,000 coronavirus testing kits to the United States on Tuesday in the first such shipment following a request from US President Donald Trump, a Seoul official told Reuters news agency on Monday.
At the same time, government leaders have called on South Koreans to continue to follow guidelines and restrictions on social gatherings, but hinted that such measures could soon be eased.
At a meeting on disaster management on Monday, Prime Minister Chung Sye-kyun said the government would soon be looking to loosen the guidelines, which call for people to stay at home, avoid social gatherings of any type, and only go out for essential reasons.
"Later this week, we plan to review our intensive social distancing campaign that we have carried out so far and discuss whether we will switch to routine safety measures," he said.
Chung cautioned that even when the restrictions are eased, the country will not return to life as before the outbreak.
"We need a very cautious approach because any premature easing of social distancing could bring irreversible consequences, and have to ponder deeply about when and how we switch to the new system," he said.