These developments could also hold significant implications for the effectiveness of any future vaccines, though experts say there would need to be many more cases of reinfection for these fears to be justified.
Two patients in Europe have been reinfected with Covid-19, according to reports, raising concerns over the longevity of natural immunity against the virus.
This comes after scientists proved that a Hong Kong man had been infected twice by different strains of the coronavirus, just months apart.
Dutch broadcaster NOS cited virologist Marion Koopmans as saying the Dutch patient was an older person with a weakened immune system.
Ms Koopmans, an adviser to the Dutch government, said reinfections had been expected.
“That someone would pop up with a reinfection, it doesn’t make me nervous,” she said. “We have to see whether it happens often.”
Dutch Health Ministry officials have not yet provided any comment on the case.
The Belgian case was a woman who had contracted Covid-19 for the first time in March and then a second time in June.
Belgian virologist Marc Van Ranst told Belgian broadcaster VRT that the woman, whose symptoms were relatively mild, may not have created enough antibodies to prevent a reinfection, although they might have helped limit the sickness.
“I think that in the coming days that we will see other similar stories… These could be exceptions, but do exist and it’s not just one,” Mr Van Ranst said. “It’s not good news.”
In the Hong Kong case, gene sequencing was carried out to prove that the man had been infected with two different strains of Sars-CoV-2.
The same sequencing was applied for the Dutch and Belgian patients, as confirmed to The Independent by Ms Koopmans and Mr Van Ranst.
There have already been a number of reports of patients being reinfected with the virus, but these were based on clinical features of the disease.
In some cases, lingering residue from the virus has returned false positives in people, while flare-ups have also been reported in those individuals who have been sick with Covid-19 for a prolonged period of time.
Addressing the reported reinfection in Hong Kong, Dr Jeffrey Barrett, from the Wellcome Sanger Institute, called for caution and said that it was hard to draw conclusions until the full research study had been published.
“This is certainly stronger evidence of reinfection than some of the previous reports because it uses the genome sequence of the virus to separate the two infections,” he said. “It seems much more likely that this patient has two distinct infections than a single infection followed by a relapse.
“An important point about this one case, which is not mentioned in the press release, is that the second infection is asymptomatic. It was caught by screening tests on returning passengers at HK airport, and the individual never developed any symptoms from their second infection.”
