Last month, Japanese authorities said a woman who had had the virus, and been declared virus-free, had tested positive again.

Medical experts have addressed concerns over whether those who have had Covid-19 can get it a second time.

The UK government's chief scientific advisor, Sir Patrick Vallance, and Prof Chris Whitty, Boris Johnson's chief medical advisor, sought to reassure the public on Monday, the Guardian reported.

They said those who have had the virus once will develop some immunity.

It was rare to get an infectious disease again, they said.

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The questions first arose last month, after Japanese authorities said a woman who had had the virus and been declared virus-free, had tested positive again.

Scientists were left confused by the news and also uneasy.

Prof Mark Harris, an expert in virology at Leeds University, said reinfection, in that case, was “unlikely”, but added that “there is some evidence in the scientific literature for persistent infections of animal coronaviruses (mainly in bats)”.

When Vallance was asked on Monday if the Japanese case meant herd immunity was no longer achievable, he replied that some people do catch infectious diseases a second time, but that it is a rare occurrence.

There was no evidence to suggest that it would occur with the coronavirus, he added.

Prof Whitty explained that with diseases, even if there is no long-term immunity, there is normally some short-term immunity.

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Prof Jon Cohen, emeritus professor of infectious diseases at Brighton and Sussex Medical School, said: “The answer is that we simply don’t know (about reinfection) yet because we don’t have an antibody test for the infection, although we will have soon.

“However, it is very likely, based on other viral infections, that yes, once a person has had the infection they will generally be immune and won’t get it again.

"There will always be the odd exception, but that is certainly a reasonable expectation.”