RResearchers in Hong Kong on Monday reported what appears to be the first confirmed case of Covid-19 reinfection, a 33-year-old man who was first infected by SARS-CoV-2 in late March and then, four and a half months later , apparently the virus re-emerged while traveling in Europe.
The case raises questions about the sustainability of immune protection by the coronavirus. But it was also struck with caution by other scientists, who questioned the extent to which the case pointed to broader concerns about reinfection.
There have been widespread reports of cases of Covid-19 reinfection. However, these reports are based on anecdotal evidence and are largely attributed to testing errors.
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But in this case, researchers at the University of Hong Kong pursued the virus from the patient’s two infections and found that they did not match, indicating that the second infection was not linked to the first. There was a difference of 24 nucleotides – the ‘letters’ that make up the RNA of the virus – between the two infections.
“This is the world’s first documentation of a patient recovering from Covid-19 but receiving another episode of Covid-19,” the researchers said in a statement.
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Experts warned that the case of this patient could be an outlier among the tens of millions of cases around the world and that immune protection can generally last longer than just a few months. They said ongoing studies following patients recovering from Covid-19 would help to reach more definitive conclusions.
“More than 24 million cases have been reported so far,” Maria Van Kerkhove, a coronavirus expert at the World Health Organization, said at a briefing on Monday when asked about the Hong Kong paper. “And we have to look at such a thing at such a population level.”
The question of how long someone has been protected against Covid-19 after being infected and brought back.
Studies are increasingly finding that most people who recover from the disease achieve a robust immune response with both antibodies (molecules that can block the virus from re-infecting cells) and T cells (which can help clear the virus) ). This has suggested that people would protect for another time for another cause.
But based on what happens to other coronaviruses, experts knew that immunity to SARS-CoV-2 would not last forever. People generally become susceptible to the coronaviruses that cause the fever after a year or even less, while protection against SARS-1 and MERS seems to last for a few years.
“What we learn about infection is that people develop an immune response, and what is not yet completely clear is how strong that immune response is and how long that immune response lasts,” Van Kerkhove said. She added that she was still investigating the Hong Kong case.
The strength and sustainability of the immune response is also a crucial factor in how long vaccines will be effective for, and for how often people may need a booster dose.
In the Hong Kong case, the man had traveled to Spain and returned to Hong Kong via the United Kingdom. A saliva sample was taken on arrival in Hong Kong as part of a screening protocol and positive testing for SARS-CoV-2 on 15 August.
During his second infection, the man had no symptoms. Some patients go through their course of Covid-19 without showing symptoms, but researchers also hypothesize that secondary cases of the coronavirus will generally be milder than the first. Even if the immune system cannot stop the virus from infecting cells, they can still respond to something that makes us sure of it. During his first case, the patient had classic Covid-19 symptoms of cough, fever, sore throat and headache.
Experts said it was also important to consider the immune response that the patient generated after his initial infection. While most people seem to increase a solid response, it has been shown that some people do not produce neutralizing antibodies – those that can block the virus from infecting cells – at very high levels, for unclear reasons.
“The fact that one can re-infect is not surprising,” said Malik Peiris, a virologist at the University of Hong Kong who is not the author of the paper describing the reinfection but is familiar with the matter. “But the reinfection does not cause disease, so that’s the first point. And the second thing is that it is important to know whether the patient mounted a neutralizing anti-inflammatory response on the first infection or not. Because the vast majority of patients in our experience have a good neutralizing anti-inflammatory response. Is this person an outlier or is he probably the average person who is infected? “
Even if the Hong Kong case is an outlier, it points to a few implications: for one, people who recovered from Covid-19 would also have to be vaccinated, the researchers said. And they need to continue with precautionary measures such as wearing a mask and physical distance.
Helen Branswell contributed reporting.
