Covid-19 CAN strike twice: 33-year-old man in Hong Kong is the first person to get reinfected

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

The healthy 33-year-old patient tested positive for the coronavirus after a mild bout of the disease four months before.

Genetic analysis revealed the second infection was caused by a different strain of the coronavirus than the first, after he returned from a trip in Spain.

The coronavirus mutates as it spreads round the globe, and these can be detected in genetic sequencing.  

Doctors warned their findings prove ‘re-infection can occur just a few months after recovery’.

They said it was likely because immunity is short lives and antibodies against Covid-19 wane quickly.

However, the man did not have symptoms of Covid-19 the second time – he had been discovered through screening at an airport.

This may suggest he had some level of immunity that protected him from severe disease.

There have been a handful of reports claiming people have been struck with the coronavirus twice.

But until now, scientists have said it was likely a fault with testing, or that inactive particles of the virus are still present in the body.

Reinfections would hinder global efforts to contain the virus. But academics said this one singular report does not prove they occur. 

Researchers from the Li Ka Shing Faculty of Medicine, The University of Hong Kong (HKU) report they are the first to prove a second re-infection of the coronavirus.

In a press release, they described how an ‘apparently young and healthy patient had a second episode of Covid-19 infection’.

The man, from Hong Kong, was first diagnosed on March 26 suffering with 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 the 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, but it may have been due to his rare circumstances.

The researchers, led by Dr Kelvin Kai-Wang To, took saliva samples from both periods of infection and ran it through genetic sequencing. 

It allows researchers to identify how many mutations the virus had accumulated in both the first and second instance.

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

The press release said: ‘The team showed that 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 virus is most likely related to strains from the US or England collected in March and April, while the second was most similar to strains in Switzerland and England found between July and August.

Viral genomes from the first and second infections had 24 differences in acids that form the viruses’ DNA.

‘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 because his immune system had already forgotten the coronavirus entirely, suggesting short-lived immunity. 

On the other hand, the 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 FMedSci, a senior scientific consultant for COVID-19 Genome Project, Wellcome Sanger Institute, Hinxton, 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 a 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 that surprising even if it is a very rare occurrence’. 

Dr Simon Clarke, Associate Professor 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 is ‘nothing to be shocked or surprised about’.

Until now, it has been unclear if people can 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. 

Common cold coronaviruses are known to cause reinfections in 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, also human coronaviruses, which seemed to produce longer-lasting immunity.

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

There have been previous alarms about second Covid-19 infections in the past. But they were not solid in their evidence.

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, Oh Myoung-don, who leads The Central Clinical Committee for Emerging Disease Control, said the flurry of cases were due to a testing fault – and not a short-lived immunity. 

The infectious disease expert revealed dead virus fragments can remain in the body, possibly for months.

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

A Japanese man in his 70s tested positive for coronavirus a second time, in March, after initially being infected while on board the disease-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.