Nevertheless, the patient developed detectable antibodies after the second infection, in what experts called an encouraging sign.
In the Netherlands, Marion Koopmans, a virologist who is Head of the Erasmus MC Department of Viroscience, said an elderly patient had also been reinfected with the virus.
But the paper, published in the journal Clinical Infectious Diseases on Tuesday, raises questions about the durability of immunity to the disease, which could have implications for policymakers and vaccine researchers, they said, while warning that broad conclusions shouldn't be drawn from one case.
Marc Van Ranst, also a virologist, told Belgian broadcaster VRT: "I think that in the coming days that we will see other similar stories".
"It's not surprising that we're seeing someone who has been infected a second time".
She said that cases where people have been sick with the virus a long time and it then flares up are better known.
"We hope that that's a lasting trend in people who are reinfected", he added. They analyzed samples taken both times the man was infected and identified significant genetic differences between them, suggesting that there were two distinct infections.
Dutch national broadcaster NOS reported the two re-infection cases this morning, citing the claims of leading virologists.
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But those cases have not been considered confirmed reinfections because less time elapsed between the positive tests, and scientists did not do a genetic sequence of the viruses.
Experts cautioned that this patient's case could be an outlier among the tens of millions of cases around the world and that immune protection may generally last longer than just a few months.
While he had a fever, cough, and headaches during his first COVID-19 illness, the man had no symptoms during his second infection. Our discoveries propose that SARS-CoV-2 may endure in the worldwide human population as is the case for other common-cold allied human coronaviruses.
'There is a lot of experience doing that with influenza where we have to change the vaccine every year because that virus changes every year.
These three cases, then, aren't a reason to panic.
"That someone would pop up with a reinfection, it doesn't make me nervous", said Koopmans. 'We have to see whether it happens often'.
The COVID-19 pandemic is still expanding, but the rise in cases and deaths has slowed globally, except for Southeast Asia and the eastern Mediterranean regions, the World Health Organization said.
Sarah Palmer, co-director of the Centre for Virus Research at the Westmead Institute for Medical Research, also urged policymakers to "underscore the need for continuing strict preventative measures until an effective vaccine is available and widely distributed".