How worrying are reports the first person in the world has been reinfected with coronavirus?

A Hong Kong man who recovered from COVID-19 became infected again four-and-a-half months later in the first documented instance of human reinfection, according to scientists.

The patient had appeared to be previously healthy, researchers at the University of Hong Kong said in a paper published in the medical journal Clinical Infectious Diseases.

The man, a 33-year-old, was cleared of the virus and discharged from a hospital in April, but tested positive again after returning from Spain via the UK on 15 August, following a saliva test at Hong Kong airport.

Some scientists have said that because it is not clear whether the man had contracted the virus again after full recovery, it could be that the sample detected traces of the virus from the initial infection in his body.

Researchers sequenced the virus from the patient’s two infections and found that they did not match, indicating the second infection was not tied to the first.

He remained asymptomatic for the second infection.

What’s important to note, is that scientists believe this could be a sign that subsequent infections do not cause as severe an illness as the first episode because of some degree of residual immunity – which may not be sufficient to stop the infection but be enough to reduce the risk of severe illness.

The new report has been greeted cautiously by scientists, with many stating it is too early to tell what the significance of the findings are yet.

Why is this report important?

The first reported case of re-infection raises questions about the durability of immune protection from the coronavirus.

There have been unverified reports of reinfection in China, but this is the first proven case of COVID-19 reinfection.

The finding suggests that some patients who recover from COVID-19, may only have short-lived immunity, suggesting that they may need vaccines after a certain amount of time has passed, like the yearly flu jab.

The case will likely also be significant for scientists who have been working on treatments using antibodies from recovered coronavirus patients.

Read more: Hong Kong to offer free coronavirus testing for all residents

It will also provide clues to how long vaccines will be effective for, and how often people might need a booster dose.

The World Health Organization (WHO) warns it is important not to jump to conclusions based on the case of one patient.

The scientists warn that reinfection is common with other coronaviruses, although other experts say reinfections may be rare and not necessarily serious.

But experts had hoped that the new coronavirus might behave more like its cousins SARS and MERS, which seemed to produce protection lasting a few years.

“The finding does not mean taking vaccines will be useless," Dr Kai-Wang To, one of the leading authors of the paper, told Reuters.

"Immunity induced by vaccination can be different from those induced by natural infection," Dr To said. "[We] will need to wait for the results of the vaccine trials to see if how effective vaccines are."

Professor Paul Hunter, professor in medicine at The Norwich School of Medicine, said that immunity was always unlikely.

“Commentators have been saying for some time that immunity is unlikely to be permanent and may only last a few months.

Read more: Third of Britons say they may not take coronavirus vaccine

Given the different intensity of the antibody response in people with mild or severe illness and the subsequent decay in levels, it is likely that those with a mild illness will have a shorter duration of immunity than those with severe illness.

For example, those infected develop an immune response as their bodies fight off the virus which helps to protect them against it returning.

The strongest immune response has been found in the most seriously-ill patients.

‘No cause for alarm’

WHO epidemiologist Maria Van Kerkhove said on Monday that there was no need to jump to any conclusions in response to the Hong Kong case.

Instances of people discharged from hospitals and testing positive again for COVID-19 infection have been reported in mainland China.

However, in those cases it was not clear whether they had contracted the virus again after full recovery – as happened with the Hong Kong patient – or still had the virus in their body from the initial infection.

Professor Brendan Wren, professor of microbial pathogenesis at the London School of Hygiene & Tropical Medicine, said: “With over 3 million cases of COVID-19 worldwide, the first reported case of a potential re-infection with SARS-CoV-2 needs to be taken into context.

“It appears that the young and healthy adult has been re-infected with a slight SARS-CoV-2 variant from the initial infection three months previously.

“It is to be expected that the virus will naturally mutate over time. This is a very rare example of re-infection and it should not negate the global drive to develop COVID-19 vaccines.”

Read more: Dominic Raab slams Russia over alleged coronavirus vaccine theft

Akiko Iwasaki, a professor of immunobiology at Yale University, tweeted shortly after the study was released that the study did not show anything unexpected.

"This is no cause for alarm - this is a textbook example of how immunity should work," she wrote.

'A worrying finding for several reasons'

It’s still unclear how rare or common reinfection from the new coronavirus might be, because few researchers have sequenced the virus from each infection.

“We’ve had, what, 23 million cases documented thus far, but the fact that one out of them at this point has been reinfected should not cause undue alarm as of yet,” said Jeffrey Shaman, an epidemiologist at Columbia University in New York.

“However, it remains very, very concerning — and this does nothing to dispel that — that we may be subject to repeat infection with this virus,” he said.

Read more: Head of UK vaccines taskforce 'optimistic' we could have drug by the end of the year

Dr David Strain, clinical senior lecturer at the University of Exeter and chair of the British Medical Association’s Medical Academic Staff Committee, said: “This is a worrying finding for several reasons.

“The first, as is laid out in this manuscript, is that it suggests that previous infection is not protective. The second is that it raises the possibility that vaccinations may not provide the hope that we have been waiting for.

“Vaccinations work by simulating infection to the body, thereby allowing the body to develop antibodies. If antibodies don't provide lasting protection, we will need to revert to a strategy of viral near-elimination in order to return to a more normal life.”

Coronavirus: what happened today
Click here to sign up to the latest news and information with our daily Catch-up newsletter