Researchers in Hong Kong say they have documented the first instance of a man who was reinfected after first contracting the novel coronavirus more than four months ago.
The researchers at the University of Hong Kong on Monday said their findings indicate the disease, which has killed more than 800,000 people worldwide, may continue to spread globally despite developing herd immunity.
The 33-year-old male was cleared of COVID-19 infection and discharged from a hospital in April, but tested positive again after returning from Spain via the United Kingdom on August 15.
The patient had appeared to be previously healthy, researchers said in the paper, which has been accepted by the international medical journal Clinical Infectious Diseases.
He was found to have contracted a different coronavirus strain from the one he had previously contracted, and remained asymptomatic during the second infection.
“The finding does not mean taking vaccines will be useless,” Dr Kai-Wang To, one of the leading authors of the research paper, told the Reuters news agency.
“Immunity induced by vaccination can be different from those induced by natural infection,” To said. “We will need to wait for the results of the vaccine trials to see how effective vaccines are.”
The researchers suggested the patients, who have recovered after getting coronavirus, should also wear masks and maintain physical distancing.
In response to the Hong Kong case, the World Health Organization (WHO) epidemiologist Maria Van Kerkhove on Monday said there was no need to jump to any conclusions.
Instances of people discharged from hospitals and testing positive again for COVID-19 infection have been reported in mainland China.
However, in those cases, it was not clear whether they had contracted the virus again after full recovery – as happened to the Hong Kong patient – or still had the virus in their body from the initial infection.
The preliminary number of patients in China who tested positive again after being discharged from hospital was 5-15 percent, Wang Guiqiang, an infectious disease specialist in China’s expert group for COVID-19 treatment, said during a press briefing in May.
One explanation was that the virus still existed in the lungs of patients but was not detected in samples taken from upper parts of the respiratory tract, he said, adding that other possible causes were low sensitivity of tests and weak immunity that could lead to persistent positive results.
Jeffrey Barrett, an expert and consultant with the COVID-19 Genome Project at the UK’s Wellcome Sanger Institute, said in emailed comments to Reuters that it was very hard to make any strong inference from a single observation.
“Given the number of global infections to date, seeing one case of re-infection is not that surprising, even if it is a very rare occurrence,” he said.