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China has discovered that roughly 14% of patients who recover from coronavirus test positive for the killer disease again – with the mechanism behind the virus' apparent ability to re-infect a complete mystery.

This comes after Japan reported that a female tour-bus guide aged in her 40s had tested positive for the COVID-19 virus for a second time in Osaka.

Normally, when you overcome a virus you gain immunity for a while afterwards which is why it is so rare for children to get chickenpox twice.

The statistics from China came from reports from hospitals in Guangdong province.

(Image: Getty)

A positive test means the “recovered” patients may still be carrying the virus, straitstimes.com reports.

Currently, scientists do not know why it happens and whether these patients could still be infectious, said Song Tie, deputy director of the Guangdong Centre of Disease Control and Prevention.

It is thought that the patients may still be fighting-off lung infections and are not yet completely healthy, Song added.

Patients are considered “recovered” when throat and nose swabs are negative in two consecutive tests, a CT scan is negative for lung lesions, and they have no fever or other symptoms, according to COVID-19 guidelines by the National Health Commission.

Dr Babak Ashrafi, at UK-based online doctor Zava, told Metro.co.uk: “Experts are busy gathering information from those who have become infected to see how well their immune systems react and how long they’ll remain immune.

(Image: SIPA USA/PA Images)

“We do know that when you catch a virus, your body learns how to fight it off.

“However, like our minds, our bodies can forget over time how to do this and immunity can wear off over time after initial infection.”

Another theory is that the original tests which said the patients had fully recovered were wrong – but that also raises concerns about containing the virus.