15-08-2020 by Mirai
In theory, after a primary infection, the patient develops protective antibodies that ensure immunity. But in the case of Covid-19, several unanswered questions remain: how long do these antibodies protect us? Are there cases of reinfection or is it more of patients with "long forms" of the disease?
What do we know about the shelf life of specific antibodies against SARS-CoV-2?
In theory, a person who is already infected with a virus is immune to it. When our body comes into contact with a virus, it develops specific antibodies that are able to recognize and fight the virus more effectively when faced with it again. It is also on this principle that vaccination and "herd immunity" are based: when 60% of the population has been in contact with the virus, its reproduction rate (the number of people infected by a patient), falls to 1 and the epidemic is no longer spreading, explains mathematician and epidemiologist Jean-Stéphane Dhersin, on the 20-minute site.
In the case of SARS-CoV-2, a shadow could add to the image:
"Unfortunately, it appears that people infected with the coronavirus gradually lose their antibodies," says Dr. Pierre Zachary.
And the specialist continues: "It is likely that you will lose your antibodies, more or less quickly depending on the severity of the disease at the beginning. People who quickly lose their antibodies could have suffered less symptomatic or even asymptomatic forms of the disease." In contrast, highly symptomatic patients, or those who have been hospitalized in intensive care, may lose their antibodies less quickly. ”A potentially dramatic finding for vaccination.
Last March, a Chinese study (published in the journal BioRxiv) looked at the likelihood of reinfection with SARS-CoV-2. Scientists inoculated officially recovered macaques with the coronavirus a second time. The animals reportedly did not develop symptoms of the disease or a new viral load, "suggesting that a primary infection protects against the virus," they said.
And other coronaviruses?
According to a study (published in October 2007 in the journal Emerging Infectious Diseases) on the SARS epidemic that hit China in 2003, the level of antibodies produced specifically against SARS-CoV-1 remains stable for approximately two years, before drop dramatically in the third year, "suggesting that reinfection would be possible after three years." However, no patient reinfected with SARS-CoV1 has been reported.
The coronavirus could remain "inactive" in the body
However, some apparent cases of reinfection with the coronavirus in patients who had initially recovered have raised concern (especially in China and Japan). Several hypotheses could explain this phenomenon: a failure of the screening tests, the possibility that the samples are poorly preserved or that the viral load is insufficient to be detected.
But the most likely hypothesis is that the patients in question would suffer a prolonged infection with the coronavirus, not a reinfection. In other words, the virus would still be present in your body undetected and could be "reactivated", for example due to a related disease. Here again, Dr. Zachary insists on the precautionary principle:
"Some patients may show expression of the virus for several months: among our patients, some tested positive in March and still were in June. Is it still the same infection? Is it a reinfection? It is very difficult to tell at this time. It is conceivable that patients who have suffered a very mild symptomatic form (with very little immune stigma) can be re-infected if conditions are unfavorable. "
The cellular immunity track against SARS-CoV-2
A study recently carried out in collaboration between the University Hospital of Strasbourg and Rouen (the results of which were published on June 22 in the journal MedRxiv) seems to indicate that our body is capable of accumulating cellular immunity against coronavirus.
Scientists have sought to understand why some people in contact with positive patients for Covid-19 show typical symptoms of the disease and, despite everything, a negative serology. Therefore, they studied the humoral and cellular immune response in 17 volunteers belonging to 7 different families. (In each family there was at least one person who developed the disease and was not hospitalized.)
Conclusions
All Covid-19 patients developed a T-cell response against various SARS-CoV-2 antigens, detectable up to 69 days after symptoms. The contact persons of these patients maintained a negative serology but developed an immune response.
Cellular structure with a frequency of T lymphocytes (white blood cells present in the blood and whose function is to defend the body against infectious attacks) equivalent to that of patients with Covid-19 and higher than those of control subjects.
"This tends to show that a transient SARS-CoV-2 infection has occurred in these people and that the cellular immune response would be more sensitive than antibodies to demonstrate SARS-CoV-2 infection," the researchers conclude.
"This is a path that looks quite promising," says Dr. Zachary. If these people with cellular immunity ever come across the coronavirus, they will likely fight the infection more effectively. "
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