HONG KONG — Researchers in Hong Kong on Monday reported about a healthy man in his 30s, contracting the coronavirus infection again four and a half months after his first bout in what appears to be the first confirmed case of COVID-19 reinfection.

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

There have been scattered reports of cases of coronavirus reinfection. Those reports, though, have been based on anecdotal evidence and largely attributed to flaws in testing.

But in this case, researchers at the University of Hong Kong said genome sequencing showed the two strains of the virus are "clearly different. There was a difference of 24 nucleotides — the “letters” that make up the virus’ RNA — between the two infections.

“This is the world’s first documentation of a patient who recovered from coronavirus but got another episode of COVID-19 afterward,” the researchers said in a statement.

There have been more than 23 million cases of coronavirus infection around the world.

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.

But it is still not clear how strong this protection or immunity is — or how long it lasts.

And the World Health Organization said larger studies over time of people who had previously had coronavirus were needed to find out more. — Agencies