On August 24, Hong Kong scientists confirmed what appears to be “the first instance of human reinfection” with the novel coronavirus (SARS-Cov-2). The 33-year-old man was reinfected for a second time with a different strain of the coronavirus more than four months after the first episode.
Previous anecdotal reports of patients testing positive in two separate tests taken weeks apart have been dismissed as false positives or remnants of the initial infection. This time, the researchers from the University of Hong Kong genetically tested the viruses from the two separate infections and found that the sequences did not match. Therefore, they claim the positive test result could not have been caused the virus simply lingering in the man’s body – which has also been observed in rare cases – since the reinfection was, in fact, caused by a different strain of the coronavirus.
The findings highlight what many scientists have emphasised all along: it should not be assumed that people who recover from the virus are immune – they should still comply with preventative measures, like wearing a mask and practising social distancing, and be provided with a vaccine once one becomes available.
The reinfection event has cast some doubt on whether people develop and retain antibodies against COVID-19 after infection. However, the man, who had only a mild infection initially – a fever, cough, sore throat, and headache that lasted a few days – did not have any symptoms the second time, suggesting his immune system may have some ‘memory’ of the previous infection, allowing it to keep the virus in check. The reinfection was discovered only because he had travelled to Spain and upon his return to Hong Kong was asked for a saliva sample as part of the coronavirus screening protocol.
In a signed statement published in the South China Morning Post, Prof Kwok-Yung Yuen, Prof Kelvin Kai-Wang To, and Prof Ivan Fan-Ngai Hung said: “This is the world’s first documentation of a patient who recovered from Covid-19 but got another episode of Covid-19 afterwards”.
They added that: “Our findings suggest that Covid-19 may persist in the global human population, as is the case for other common-cold associated human coronaviruses, even if patients have acquired immunity via natural infection”.
At a briefing on Monday, Dr Maria Van Kerkhove of the World Health Organization, who reported that the number of cases has now reached 24 million, also said: “We need to look at something like this at a population level.” After a year or possibly less, people become susceptible again to other coronaviruses, such as those that cause the common cold, so it is unlikely that any potential immunity to SARS-CoV-2 will last for life.
“What we are learning about infection is that people do develop an immune response, and what is not completely clear yet is how strong that immune response is and for how long that immune response lasts”, said Van Kerkhove.
Upon reviewing the case, Dr Akiko Iwasaki, an immunologist at Yale University who was not involved with the work, told the New York Times: “It’s kind of a textbook example of how immunity should work.” She explained that “natural infection created immunity that prevented disease but not reinfection”, adding that “in order to provide herd immunity, a potent vaccine is needed to induce immunity that prevents both reinfection and disease”.