Can the coronavirus infect someone twice?

According to the South China Morning Post, up to 10% of coronavirus patients leaving Wuhan medical facilities after being tested negative for Covid-19 appear to have been subsequently re-infected. It is not the first time infection. Nevertheless, scientists say it is unlikely that the virus will strike twice.

Wuhan doctors are puzzled. Health workers in this central Chinese city where the coronavirus first appearedobservedseveral cases where patients left the hospital without leaving any traces of virus in their bodies and then tested positive for coronavirus a second time.

In total, up to 10% of patients with coronavirus seem to have been “re-infected”, according to a hospital and several quarantine centers in Wuhan, where daily life is gradually returning to normal after several months of confinement.

Tongji Hospital – where the first cases of Covid-19 were detected – announced that out of 147 patients discharged during the week, five were again positive; that is to say 3%. This was the case for a higher proportion of patients in quarantine centers, this figure varying from 5 to 10%.

Defy the laws of virology?

It is not the first time that the coronavirus appears to infect the same person twice. At the end of February, a 40-year-old woman was tested positive ten days after leaving a health center in the Japanese city of Osaka, after having apparently been “cured”. At the same time, a Chinese man from Jiangsu Province who had officially recovered from the coronavirus was admitted to hospital three days later, after being “re-infected”.

These many potential cases of “reinfection” have left scientists puzzled. These examples seem to suggest that Covid-19 works differently from its predecessors, SARS and MERS-CoV. These two viruses have never infected the same person twice. Any virus that does this would be against the laws of virology. It goes without saying that this would also pose a major health problem.

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“During a viral infection, the patient’s body develops antibodies that are very specific to the virus that infected them – and after they heal, these antibodies do not go away,” said Robin May, professor of infectious diseases and director. from the Institute of Microbiology and Infection at the University of Birmingham.

“They go into hibernation and are ready to wake up as soon as the same pathogen tries to contaminate the body again. This characteristic of the immune system is the same against all known viruses. “

Research on Covid-19 suggests that this immune mechanism works. “The data we get from China shows that infected patients develop many antibodies that are probably doing their job to protect the body,” added Olivier Terrier, virologist at the French Research Institute of CNRS, the International Center for Research on infectious diseases of Lyon.

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“From a scientific point of view,” added May, “there is no sign at this stage that there could be an infection.”

One of the remaining uncertainties concerns the time during which the antibodies work as a barrier against disease. “These cells typically do this job for a period of weeks to months – and in the case of other coronaviruses, this immunity lasts a long time,” said Terrier.

Questions about test reliability

In the reported cases of “re-infections”, those affected had been tested within days of discharge from hospital, which precludes the possibility that ineffective antibodies may appear to have contracted the coronavirus a second time.

There must therefore be another reason for this phenomenon of positive tests in patients who have “recovered”. These incidents “raised the question of whether nucleic acid tests may not be reliable for detecting traces of the virus in some of the recovered patients”, theSouth China Morning Postobserved.

“It is possible that the concentration of the virus in the body of these people is too low to be detected and that, for one reason or another, the disease has started again,” said Terrier. “The fact that these people appear to have infected no one else reinforces the assumption that there is still a tiny bit of virus left in their bodies,” added May.

The other potential explanation is that these coronavirus patients “may have problems with their immune systems, so they did not produce the appropriate antibodies,” said Terrier.

This is one of the reasons why he argues that more research is needed on the immune response to the coronavirus. “We are only beginning to understand how it works,” he said. This work would help refine the identification of groups at risk, as well as potentially open up new avenues in the search for effective treatments and vaccines.

A better understanding of the immune response could also help if the issue of repeated infection comes up with a mutation of the virus. “If the pathogen changes so that the body no longer recognizes it, the virus can infect someone twice,” said May. The same thing happens with the flu: “People don’t get the same strain twice, but they can get it the next year after a slight mutation of the virus,” he said. Coronaviruses are known for their tendency to mutate – although for now the one who hails from Wuhan to take the world by storm has not undergone such a change.

While it certainly seems scientifically unlikely, the notion of a single virus that infects the same person twice is instructive. He warns of blind confidence in screening tests and stresses the importance of monitoring patients who appear to be cured.

This article was adapted from the original in French.