They explained that these results indicate that the disease, which has killed more than 800 thousand people around the world, may continue to spread among the Earth’s population despite the herd immunity.
The patient, a 33-year-old man, recovered from Covid-19 and was discharged from hospital in April, but tested positive again after his return from Spain via Britain on August 15.
In the paper, which was accepted by the International Journal of Clinical Infectious Diseases International, the researchers said the patient appeared to have previously been in good health.
And he was found to have contracted a different strain of Corona virus than the one he had previously infected with, and his infection remained asymptomatic in the second infection.
“The results do not mean that vaccinations will be useless. The immunity that results from vaccination can be different from that caused by natural infection,” Kai-Wang Tu, one of the paper’s senior authors, told Reuters.
“We will need to wait for the results of the vaccine trials to see how effective the vaccines are.”
There is no need to jump to any conclusions regarding the Hong Kong case, said Maria Van Kerkhove, an epidemiologist with the World Health Organization.
Cases have been recorded of people discharged from hospitals and tested positive again for Covid-19 infection in mainland China. However, it was not clear in those cases whether the patients contracted the virus again after complete recovery, as happened to the Hong Kong patient, or the remnants of the virus were still in their bodies from the first infection.
Wang Guiqiang, an infectious disease specialist with a group of experts in treating COVID-19, said at a press conference in May that the initial number in China of patients who tested positive again after being discharged from hospitals was between 5 and 15 percent.
He added that one of the explanations is that the virus was still present in the lungs of patients, but it was not detected in samples taken from the upper parts of the respiratory system.
Another possible reason, he added, is the low degree of sensitivity to tests and weak immunity, which could lead to continued positive results.
Jeffrey Barrett, an expert and consultant on the Covid-19 genome project at Britain’s Wellcome Sanger Institute, said in emailed comments to Reuters that it was very difficult to draw any solid conclusion from observing a single case.
He added, “Given the number of injuries in the world so far, seeing one case re-infected is not a surprise, even if it is rare.”