Fifty-one people who recovered from coronavirus in South Korea have tested positive again – raising fears the virus can be reactivated.
The patients – from the country’s worst-hit City, Daegu – were put in quarantine after being diagnosed with the virus, then tested positive again days after being released.
Korea’s Centers for Disease Control and Prevention (KCDC) said the virus was likely ‘reactivated’, rather than patients becoming re-infected.
Scientists at the Government-run health body believe the virus may lay dormant at undetectable levels in human cells.
They say that for unknown reasons the viral particles can then be reactivated and start attacking the lungs once more.
But there is no evidence to prove that the virus acts in this way and studies in monkeys have actually shown the opposite.
Experts say in cases where patients produce a positive result twice, it is normally because of a test giving the wrong result, which happens one in five times.
Paul Hunter, an infectious diseases professor at the University of East Anglia, told MailOnline: ‘I agree that these will not be reinfections but I do not think these will be reactivations.
‘Personally I think the most likely explanation is that the clearance samples were false negative.’
Professor Hunter highlighted that conventional coronavirus tests give the wrong result 20 to 30 per cent of the time.
He believes the test the South Korean patients were given before being released from quarantine wrongly showed they had recovered, when they were actually still infected.
KCDC Director-General Jeong Eun-kyeong said a team of investigators had been sent to Daegu, the region worst-hit by coronavirus, to conduct an epidemiological investigation into the cases.
South Korea recorded fewer than 50 new cases of the novel coronavirus today – the lowest daily increase since late February. It brings the nation’s total infections to 10,284.
Experts in Japan have previously expressed their concern that patients could possibly relapse, after reports of an elderly man and woman becoming reinfected.
But a study on monkeys published on March 16 showed the animals developed immunity against the virus after being infected with it in the lab.
The first known case of a person being re-diagnosed with COVID-19 was reported in Japan’s Osaka prefectural.
The woman, working as a tour bus guide in Wuhan, where the disease first emerged in December 2019, tested positive on February 26 after a negative result on February 6.
The details are sparse, but the woman had reportedly suffered no symptoms for at least a week between the two episodes.
Academics said it was a ‘concern’, but there was too little information to draw conclusions.
Professor Mark Harris, virology at University of Leeds, said: ‘The reports that patients who tested negative subsequently tested positive again is clearly of concern.
‘It is unlikely that they would have been reinfected having cleared the virus, as they would most likely have mounted an immune response to the virus that would prevent such reinfection.
‘The other possibility therefore is that they did not in fact clear the infection but remained persistently infected.’
Either the woman had indeed had a relapse of the illness, or she never actually cleared the virus from her system, leaving it detectable with later tests.
The former explanation suggests the virus is bi-phasic, meaning it appears to go away before recurring.
The latter could be due to a lack of efficient testing, which cannot clearly show if the disease has completely cleared.
‘It does appear that swabs for the virus are not 100 per cent reliable,’ Professor Paul Hunter, medicine at University of East Anglia (UEA), said. Professor Rowland Kao, Sir Timothy O’Shea Professor of Veterinary Epidemiology and Data Science, University of Edinburgh, said: ‘It would seem unlikely that this is a common occurrence, and thus should have only a small impact on the overall epidemic projections themselves.’