Researchers in Hong Kong claim to have documented the first confirmed case of coronavirus reinfection.

A 33-year-old was found to be infected with virus a second time 142 days after the original infection, report researchers from Hong Kong University.

When initially infected the man displayed symptoms of a fever, cough, sore throat and headache for three days and was subsequently hospitalised. After his symptoms cleared he was discharged two weeks later, having tested negative for the virus twice.

However, the man tested positive again more than four months later when screened at Hong Kong airport after arriving from Spain. The second infection of the virus did not cause any symptoms.

According to researchers at Hong Kong University, the viruses that caused each case of infection differed by 24 nucleotides, indicating that the man was infected twice by two different versions of SARS-CoV-2.

“Our results suggest SARS-CoV-2 may continue to circulate among humans despite herd immunity due to natural infection. Further studies of patients with re-infection will shed light on protective correlates for guiding vaccine design,” the researchers note.

Their study has been accepted for publication in Clinical Infectious Diseases.

“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,” said Dr David Strain, from the University of Exeter, as reported by The Independent.

“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.”

Others urged caution over the findings. Dr Jeffrey Barrett, from the Wellcome Sanger Institute, told the media that “seeing one case of reinfection is not that surprising even if it is a very rare occurrence,” and noted that it may turn out that “second infections, when they do occur, are not serious”, though he also pointed out that whether the man was infectious during the second episode is unknown.

Also commenting on the findings, BBC News quoted Dr Simon Clarke, associate professor in cellular microbiology at the University of Reading, as saying: “The significant thing here is that being reinfected with a mutated strain demonstrates that it is more likely to be reinfection, 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.

“The finding of a mutant strain is absolutely nothing to be shocked or surprised by. It would actually be more interesting if there were no mutations cropping up.”