You can get Covid-19 TWICE: Man in Hong Kong tests positive for a DIFFERENT strain of coronavirus four months after recovering from first infection

Covid-19 survivors can get reinfected, according to doctors in Hong Kong who say they are the first in the world to prove a patient was struck down twice. 

The 33-year-old man — who had no known underlying conditions — tested positive for the coronavirus four months after he recovered from his first bout of the life-threatening disease.

Genetic analysis revealed his second infection, which he caught on a trip to Europe, was caused by a different strain of the virus.

All viruses — including SARS-CoV-2, the virus behind the pandemic — mutate over time. Analysing the DNA of pathogens can spot any changes, which can make them weaker or deadlier.

Doctors warned their findings prove 're-infection can occur just a few months after recovery'. They said it was likely immunity is short-lived and that antibodies against Covid-19 fade quickly.

But the unidentified man did not have symptoms of Covid-19 the second time — he was only discovered through screening at an airport. This may suggest he had some level of immunity that protected him from severe disease, experts say.

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Covid-19 survivors can be reinfected twice, according to doctors in Hong Kong who report the first known case

Hopes of long-lasting immunity have been hampered in recent months by several reports that have claimed to show people being struck down with the coronavirus twice.

But until now, scientists have reiterated that cases of re-infection were more likely down to a fault with testing, or that inactive particles of the virus are still present in the body of patients months after they beat the illness.

With some illnesses such as chickenpox, the body can remember exactly how to destroy it and becomes able to fend it off before symptoms start if it gets back into the body.

Experts say short-lived immunity would hinder global efforts to contain the infection because it means patients are not protected for a long time, leaving countries at risk of a second wave of the disease this winter.  

But academics said this one singular report — which will be published in a medical journal but has not yet been published — does not prove they occur.

Researchers from the Li Ka Shing Faculty of Medicine at the University of Hong Kong say they are the first to prove a second re-infection of the coronavirus.

And they insisted the finding does not mean taking vaccines will be useless. Dr Kai-Wang To, study co-author, said: 'Immunity induced by vaccination can be different from those induced by natural infection.

'[We] will need to wait for the results of the vaccine trials to see if how effective vaccines are.'

In a press release, they described how an 'apparently young and healthy patient had a second episode of Covid-19 infection'. Reports say the man was an IT worker.

The man, of Hong Kong, was first diagnosed on March 26 after having a cough, sore throat, fever and headache, according to parts of the paper revealed by a journalist at the South China Morning Post.

He was hospitalised that day but all his symptoms subsided after three days. He was discharged on April 14 after two negative test results.

In his second episode, the man was tested on August 15 when he returned to Hong Kong from Spain via the UK. 

He was hospitalised again but did not have any symptoms. It's unclear why he was hospitalised.

The researchers, led by Dr Kelvin Kai-Wang To, took samples of his saliva both times he tested positive and analysed the genetic sequence of the strain. 

The process allows experts to identify what mutations coronavirus had accumulated over time.

These genetic variants can act as the fingerprints of the pathogen, to indicate where in the world it originated. 

The press release said: 'The team showed the genome sequence of the virus strain in the first episode of Covid-19 infection is clearly different from the genome sequence of the virus strain found during the second episode of infection.'

The first sample he had taken is most likely related to strains from the US or England collected in March and April, the academics claimed.

While the second — which was different in 24 places — was most similar to samples found circulating in Switzerland and England between July and August.

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The press release revealing the first known case of re-infection with Covid-19

'This case illustrates that re-infection can occur after just a few months of recovery from the first infection,' the researchers said.

'Our findings suggest that SARS-CoV-2 may persist in the global human population as it is the case for other common-cold associated human coronaviruses.'

The underlying reasons why the man got Covid-19 again are not clear. 

It may simply be because his immune system had already forgotten the coronavirus entirely, suggesting short-lived immunity. 

On the other hand, his lack of symptoms may suggest his immune system did recognise the coronavirus and was primed to attack, regardless of what strain it was.  

Commenting on statements made by HKU, independent scientists admitted it is the strongest evidence of re-infection yet because it used genetic sequencing.  

Dr Jeffrey Barrett, of the Wellcome Sanger Institute, said: 'This is certainly stronger evidence of re-infection than some of the previous reports because it uses the genome sequence of the virus to separate the two infections.

'It seems much more likely that this patient has two distinct infections than a single infection followed by a relapse (due to the number of genetic differences between the two sequences).'

However, he said it was very hard to draw conclusions without reading the full report. 

Dr Barrett said: 'It may be that second infections, when they do occur, are not serious (though we don’t know whether this person was infectious during their second episode).'

He added that given the number of global infections to date — 23.5million — one case of reinfection 'is not surprising even if it is a very rare occurrence'. 

Dr Simon Clarke, an expert in cellular microbiology at the University of Reading, said: 'The significant thing here is that being re-infected with a mutated strain demonstrates that it is more likely to be re-infection, rather than the same infection that has hung around because the virus has not actually been got rid of, as some people have suggested happens.'

He added that mutant strains are 'nothing to be shocked or surprised about'.

Professor Paul Hunter, of the University of East Anglia, said it was unclear whether reinfected people would pose any risk to others because they may have a smaller viral load — the amount of the virus in their body.

Dr Jonathan Stoye, of the Francis Crick Institute, called the report 'fascinating'. 

Until now, it was unclear if people could catch SARS-CoV-2 twice for a number of reasons.

It's not clear how long immunity to the virus lasts — whether it be a few months or several years — and how this differs between people. For instance, people who only get mild bouts of the disease may develop less protection than ones who were left critically-ill.

Immunity against other coronaviruses that cause the common cold is known to last less than a year, with cases spiking in the winter.

But experts had hoped that the new coronavirus might behave more like SARS and MERS, two coronaviruses that the body seems to offer longer protection against.

Scientists have found SARS patients still have crucial disease-fighting cells 17 years after infection.

Evidence is beginning to suggest that antibodies disappear in as little as eight weeks after infection with SARS-Cov-2. On the other hand, T cells - which target and destroy cells already infected with the virus - are 'durable'.

Science is still trying to answer questions about immunity but it's been challenging because the coronavirus has only been known to academics for eight months.  

Alarm bells have been raised about re-infections since the pandemic began. 

In April, South Korean officials feared a group of almost 300 people had been reinfected after the country saw the virus fizzle out. 

But later, a senior South Korean official said the flurry of cases were due to a testing fault — and not down to short-lived immunity. 

Infectious disease experts revealed that dead virus fragments can remain within the body, possibly for months.

These lingering fragments may cause a positive result, even though the person is not sick or infectious anymore.  

And in March it was revealed a Japanese man in his 70s tested positive for Covid-19 a second time. He was first infected while on board the coronavirus-ridden Diamond Princess cruise ship in February.

He tested positive two weeks after he recovered and tested negative. It is not clear how many times he had a negative result. 

It may be possible someone can test positive for longer than two weeks as their body tries to clear the virus, and the negative result was false.

A Japanese woman was also diagnosed again two weeks after her recovery. 

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.