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Hong Kong experts report first case of coronavirus reinfection, suggesting second encounter may be possible

However, the World Health Organization said it was too early to draw conclusions from a single case, calling for more studies

A man in his 30s has tested positive for the new coronavirus again after recovering from the first episode. It the world's first documented case of reinfection, according to researchers from Hong Kong. The report raises questions on whether recovered patients can stay protected from the new coronavirus.

 "Our findings suggest that SARS-CoV-2 may persist in the global human population as is the case for other common-cold associated human coronaviruses," they said in a statement. However, the World Health Organization said it was too early to draw conclusions from a single case.

The man did show any symptoms the second time. “This is no cause for alarm — this is a textbook example of how immunity should work,” Yale School of Medicine professor Akiko Iwasaki wrote in a tweet. “While immunity was not enough to block reinfection, it protected the person from the disease.”

The 30-year old tested positive for Covid-19 in the last week of March. He was subsequently hospitalized and treated. Four-and-a-half months later, he was screened for the virus at the Hong Long airport after his visit to Europe. His tests came back positive. The study is accepted for publication in the journal Clinical Infectious Diseases.

This, however, is not the first time that reports of coronavirus reinfections have surfaced, but the evidence was either flawed or anecdotal. Now, experts from Hong Kong performed genomic sequencing to study the differences between the virus strains behind the two infections.

Their analysis showed both infections were caused by different strains. “Our results prove that his second infection is caused by a new virus that he acquired recently, rather than prolonged viral shedding," Dr Kelvin Kai-Wang To, a clinical microbiologist at the University of Hong Kong, told The New York Times.

"The report from Hong Kong of a re-infection in a man by Covid-19 that was genetically different from the first infection should not be too surprising. It is, however, important that this is documented,"  Prof Paul Hunter, Professor in Medicine, The Norwich School of Medicine, University of East Anglia said in a statement distributed by the UK-based Science Media Centre.

What do these findings mean? Researchers from Hong Kong said attaining herd immunity through natural infection is unlikely to stop the pandemic. “Although it is possible that subsequent infections may be milder than the first infection, as for this patient. Covid-19 will likely continue to circulate in the human population as in the case of other human coronaviruses,” the researchers said in a report. Agreeing with them, Dr Iwasaki said that vaccination is the only safe and effective way to achieve herd immunity.

More studies needed

Experts have called for more research. "There's been more than 24 million cases reported to date. And we need to look at something like this on a population level. And so it's very important that we document this -- and that, in countries that can do this, if sequencing can be done, that would be very, very helpful. But we need to not jump to any conclusions," Maria Van Kerkhove, the World Health Organization's technical lead for coronavirus response and head of the emerging diseases and zoonoses unit, said during a press briefing.

Dr Jeffrey Barrett, a senior scientific consultant for Covid-19 Genome Project at the Wellcome Sanger Institute, also agreed. In a statement, he said, it is very hard to conclude anything from a single observation. "This may be very rare, and 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).”