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If the long covid experienced by some people remains a mystery, new studies are gradually discovering biological or immune differences in people who have suffered from it, or are still suffering from it. Discoveries that could perhaps make it possible to determine new therapeutic targets.
Why does covid have symptoms that last in some people, with after-effects (in around 10 to 30% of “covids”)? For the time being, science does not yet establish it with certainty. But a lot of research is tackling the conundrum of long covid. This is particularly the case of a study conducted jointly by Inserm with a Portuguese team, and revealed on May 3. She announces that SARS-CoV-2 could persist in the intestinal mucosa of certain patients.
Markers discovered, proof that the virus is still present
In this study, researchers studied the immune systems of 164 people six months after their infection. They analyzed the blood samples of 127 people, half of whom had a long Covid (fatigue, shortness of breath, cough, muscle or chest pain, anxiety, etc.) and 37 control people who had not been infected. The authors were particularly interested in specific immune cells: T lymphocytes (including CD8 cells) involved in the elimination of the virus and antibodies directed against SARS-CoV-2.
In addition, they had blood samples taken during the acute phase of the disease from 72 of these patients, which allowed them to retrospectively compare the level of inflammation in the early stage in people who subsequently developed Covid. long or not.
Contacted by Doctissimo, Dr Jérome Estaquier, Inserm researcher and author of this study explains to us:
“We have thus identified in people with long Covid a persistence of the virus through different markers, between 3 and 5, demonstrating that the body continues to fight: part of the lymphocytes, defense cells which serve to fight against the virus , interferences of the molecules which are induced, and also the persistence of igA type antibodies which are normally short-lived. However, six months after infection, the presence of these antibodies proves that we still have viral antigens which are produced.
Why does the virus persist in the intestinal mucous membranes?
For the researchers, this persistence at the immune level confirms observations already made: “One of the hypotheses is that people who present with a more exacerbated immunodeficiency early on develop more serious initial forms of Covid-19 and fail to effectively eliminate the virus which passes into the intestinal mucous membranes, where it settles permanently. The immune system somehow ends up tolerating it at the cost of persistence of symptoms of varying intensity and nature. explains the researcher.
Why the intestinal mucosa? “Probably because usually our immune system is not made to attack our microbial flora. Our system is rather tolerant there, the viral agents have been able to find a niche there, to remain in this favorable environment”.
Lack of vitamin D, also correlated with Covid Long?
Another study published in April suggests there may be a link between low levels of vitamin D and an increased risk of COVID in the long term.
For this study, Italian this time, the researchers examined 100 patients aged 51 to 70, with and without long COVID. They measured their vitamin D levels when first admitted to hospital with COVID-19 and six months after discharge, and found lower vitamin D levels in patients with long COVID compared to those who were spared by this persistent form. This result was more evident in patients who had symptoms of “brain fog”, such as confusion, forgetfulness and poor concentration, at the six-month follow-up.
A data that can play, for Dr Estaquier, but which is not necessarily conclusive:
“We can of course start from the principle that food, and its contributions, can intervene in the fact of developing a long covid or an infection. Now, what we’ve seen more commonly from the onset of infection, in hospitalized patients, is that their immune systems suffer. However, the establishment of immune responses is quite independent of vitamin D levels.
Be that as it may, in the opinion of the researchers involved, these two new studies still need to validate these results in new cohorts before perhaps being able to lead to specific treatment.
The long covid, a mystery soon elucidated?
Are we thus moving towards a better understanding of long covid? According to Professor Eric Caumes, infectious disease specialist to whom we asked the question, these two studies do not quite fit into the subject.
“In the study on the markers, it is not really a question of long covid but of sequelae of serious covid on hospitalized patients. The main conclusion is that the most inflammatory patients at the start are those who have the most sequelae at 6 months. But serious covid sequelae and long covid should not be mixed up.”
His analysis is even more reserved regarding the involvement of vitamin D.
“For the study on vitamin D, it refers more to the so-called long covid, in fact a set of disorders grouped under the term “functional somatic disorders” (not recognized as such by the authors). The covid only intervenes there as a triggering factor, as we see with other infectious diseases or traumas. We can’t conclude anything on that. That being said, it is better to have the correct level of vitamin D in the blood, as in other areas of life. But from there to conclude that it is associated with the long covid, there is a step that I will not take.