A Hong Kong man, who recovered from COVID-19 , was infected again four-and-a-half months later in the first documented instance of human re-infection, researchers at the University of Hong Kong said on Monday.
The findings indicate the disease, which has killed more than 8,00,000 people worldwide, may continue to spread among the global population despite herd immunity, they said.
The 33-year-old male was cleared of COVID-19 in April, but tested positive again after returning from Spain via Britain on August 15.
The patient had appeared to be previously healthy, researchers said in the paper, which was accepted by the international journal Clinical Infectious Diseases.
He was found to have contracted a different coronavirus strain from the one he had previously contracted and remained asymptomatic for the second infection.
“The finding does not mean taking vaccines will be useless,” Dr. Kai-Wang To, one of the leading authors of the paper, told Reuters. “Immunity induced by vaccination can be different from those induced by natural infection,” To said. “Will need to wait for the results of the vaccine trials to see if how effective vaccines are.”
World Health Organization (WHO) epidemiologist Maria Van Kerkhove said that 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.
The preliminary number of patients in China who tested positive again once being discharged from hospital was 5%-15%, Wang Guiqiang, an infectious disease specialist in China 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. Other possible causes were low sensitivity of tests and weak immunity that could lead to persistent positive results, he added.
