Sick one day, sick again several months later? Several cases of "recontamination" apparent to Covid-19 have been identified for several weeks, causing all people who have already been infected to fear it again. On Tuesday, the Reuters agency reported the case of a woman who tested positive in China in early August, after a first contamination in February and then recovery.
Virologist Yves Gaudin, from the Institute for Integrative Cell Biology (I2BC) at Paris-Saclay, first of all wishes to stress that “you have to be very careful with these cases of reinfection, especially since they are very rare: a few out of 20 million official cases ”.
Remember also that some cases detected may turn out to be "false positives". Even though these are very rare, they may have existed, especially at the start of the SARS-CoV-2 coronavirus pandemic. In June, “dozens of false positives” were reported in Meurthe-et-Moselle because of a poor quality reagent.
At the Henri-Mondor hospital in Créteil (Val-de-Marne), where an individual tested positive recently after a first suspicion of infection in another hospital in March, the results that came out this Friday finally reveal that the individual was falsely positive at the time. "We have very sensitive study methods making it possible to study the entire genome, which finally showed us that the subject was not infected in March", explains the head of the infectious diseases department, Jean-Daniel Lelièvre . Shortly before, the immunologist told us "to ask the question whether it could be a recontamination".
The virus still present in some organs
Because this kind of case could well arise. Among the hypotheses put forward, before talking about “recontamination” or “reinfection”, we must consider the same infection but over a long period. Indeed, "this may concern people who have never succeeded in completely eliminating the virus", underlines Yves Gaudin. “Even if the patient no longer has symptoms or fever, it cannot be ruled out that the virus may settle permanently in certain organs. It would then always be the same infection with an alternation of asymptomatic (which can be taken for a cure) and symptomatic periods, ”adds the virologist. “This is called chronic carriage. At first, an individual has a lot of viruses. And after a while, he loathes a lot less but enough to be tested positive by PCR ”, adds Jean-Daniel Lelièvre.
PODCAST. What are coronaviruses? Dive into the biology of viruses under a microscope
Which would not be an exception: Ebola virus can remain in the semen of survivors for at least twelve months after recovery, according to a study published in the Journal of Infectious Diseases.
Are the antibodies neutralizing?
Let us now move on to the hypothesis of a real new contamination. This brings us back to the question of the immunity that an organism will develop when it is targeted by a virus, and in particular antibodies. In theory, these are supposed to protect against further infection. Except that there are two pitfalls.
Newsletter - Most of the news
Every morning, the news seen by Le ParisienI'm registering
Your email address is collected by Le Parisien to enable you to receive our news and commercial offers. Learn more
On the one hand, we do not yet know precisely how long these antibodies will stay in the body. Only 16.7% of participants in a UK study had enough neutralizing antibodies 65 days after symptoms started, according to pre-released results on July 11. At the end of May, another study carried out by teams from the Strasbourg University Hospital and the Institut Pasteur on 160 patients with mild forms of Covid-19 concluded that "nearly all of the patients developed antibodies within the following 15 days the onset of infection ”. “In 98% of them, neutralizing antibodies were detected after 28 days,” added the Institut Pasteur.
“The duration of protection, objectively, we do not know. In addition, some patients hardly develop antibodies. The immune system does not respond in the same way in everyone. It may depend on genetics, general health, age, etc. ”, explains Yves Gaudin.
VIDEO. The three "big options" to make an epidemic disappear
In the case of the SARS-CoV-1 epidemic in the early 2000s, "studies had reported that 10% of patients were no longer immune after 12 months", reports Inserm. But the organization specifies that "it is however not certain that these data are applicable to SARS-CoV-2".
On the other hand, when antibodies are present in the body, "we are not sure that they are protective against a new infection", underlines Yves Gaudin.
The track of cross immunity
Antibodies are not the only possible immune response. The body can also generate T lymphocytes, which are very good cells at "eradicating" the virus when infected. “They are more likely to effectively eliminate a virus than to prevent infection,” says Jean-Daniel Lelièvre.
Some lymphocytes generated during contamination by another more banal coronavirus could even be effective against SARS-CoV-2, according to the principle of cross-immunity. Clearly, an individual who often catches colds, for example, could be more protected against Covid-19 today. However, this lead is only being studied and it does not seem conclusive in children.
Anyway, the level of the immune response would also depend on the extent of the infection the first time. “People who have had serious and very symptomatic forms will a priori be protected. It is more problematic for others, those who have had no or few symptoms, ”explains Jean Daniel Lelièvre. Moreover, the various suspected cases of “recontamination” most often concern individuals who did not contract a very serious form of Covid-19 the first time.
Nothing indicates a virus mutation
Finally, there is the risk of a mutation of the SARS-CoV-2 coronavirus. As with the flu virus, which changes every year. It could also explain why some individuals catch Covid-19 twice, but this hypothesis seems excluded by the scientific community.
“For the moment, there are local mutations in this virus, but no significant variations. There is therefore little risk that these mutations will allow the virus to escape the immune response, ”concludes Yves Gaudin.