Are patients cured of Covid-19 vaccinated? Have asymptomatics developed immunity? Are some naturally protected? We take stock.
This is one of the points that has mobilized researchers for months. Can we be immune to Covid-19? The question is simple, but science is fumbling. However, leads are starting to emerge.
But before discussing them, it should be understood that being immune does not necessarily mean being protected against the coronavirus.
“Immunity means being able to produce antibodies or killer cells against the virus. Being protected means that this immunity is capable of fighting infection, ”explains Morgane Bomsel, CNRS research director at the Institut Cochin, in Paris.
This difference in vocabulary partly explains the difficulty researchers have in understanding the disease. People who have died from Covid-19 are those who have developed an immune reaction that is too strong but whose antibodies have not, however, made it possible to slow down the infection. In this case, it is the inflammation, and not the coronavirus, which is the cause of death.
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Are we immune when we have already been infected?
It all depends on the degree of infection, because the more severe the infection, the more antibodies are produced. “For those who have had an average syndrome (ie symptomatic but which does not require hospitalization, editor’s note), we can think that there is a protective immunity “, explains Morgane Bomsel.
How long is it going to take? We do not know. The researcher expects several months, but as always, caution is in order. Science does not have enough hindsight to be able to determine the evolution of the immune response over time.
Another gray area:
In some of the patients, there is no production of antibodies and we do not know why. Maybe they’ve developed some other immunity that hasn’t been detected?
According to a study by the Swedish hospital Karolinska in early July, Covid-19 patients with few or no symptoms could develop immunity linked to T lymphocytes, a type of white blood cell responsible for the second part of the immune response (l immunity), the first coming from antibodies, even if their antibody test is negative.
Can we be protected against Covid-19 after a similar infection (cold, flu, etc.)?
This is one of the most promising avenues, but it only concerns infections linked to other coronaviruses. A study published on July 29 in the medical journal Nature points to the still poorly understood role of T lymphocytes.
Co-author of the study, German immunologist Andreas Thiel explains:
At least a third of adults who had never been in contact with SARS-CoV-2 (the virus responsible for Covid-19, editor’s note) had T lymphocytes capable of reacting to this virus. They most likely came from infections prior to other coronaviruses.
The work of a team from Singapore, made public on July 15 by Nature , had reached the same type of conclusion.
Are some naturally protected against Covid-19?
In some individuals who have never been exposed to SARS-CoV-2 , we find T lymphocytes that react to this new coronavirus as well as to four others, responsible for simple colds, reveals another study, this one American, published August 4 in the journal Science .
“This could help explain why some people with Covid-19 have few symptoms while others fall seriously ill,” said one of the authors, Daniela Weiskopf, of the institute in a statement. La Jolla immunology in California.
This study deepens other work published in mid-May by the same team in the journal Cell. They showed the presence of T lymphocytes capable of reacting to SARS-CoV-2 in 40 to 60% of people who had never been exposed to this virus.
“Whatever the mechanisms, it is very likely that there are many people immunized without being detected by serology”, that is to say by antibody tests, assures Yonathan Freund , professor of medicine at emergency at the Parisian hospital of Pitié-Salpêtrière.
Can you be infected a second time?
We still have little data on the subject. If a person comes into contact with the virus again, they can be expected to develop the same immune reaction as the first time. For those who are asymptomatic, there is no need to worry.
As for those who developed moderate or severe symptoms, the body produced an immune response in proportion. People who have survived hospitalization have therefore developed antibodies in large quantities, which should protect them against a second infection.
A few cases of recurrence would still have been detected in China. But again, the questions outnumber the answers. The reliability of this information is in doubt. “Were these people really re-infected or did they still have the virus in their body that would have reactivated? Morgane Bomsel also wonders.
“Serology tests don’t tell the whole truth, they tell it for a certain period only,” says Andreas Thiel. Studies have indeed shown that in patients affected by Covid-19, the level of antibodies could drop rapidly, within a few weeks. For Yonathan Freund, two possible explanations:
One, which would be catastrophic, is that immunity does not last in Covid. But I don’t think that’s the case: out of 18 million cases, we have never heard the slightest proven case of recurrence. The other is that there may be people who are immune that cannot be detected by serology.
Do you remain contagious when you are immune?
“The immunity you have developed is that you have too many viruses. It helps protect your cells from infection. But the virus that you disseminate nasally is not surrounded by antibodies, ”observes Morgane Bomsel.
In other words, the virus remains transmissible, not the antibodies.
The barrier gestures, therefore, continue to apply even for people who have already been infected with Covid-19.
