Allergies better equipped against Covid-19?

Researchers suggest that people with asthma would be protected from the coronavirus. However, there are still several gray areas.

Illustration of a grass pollen allergy @BelgaImage

This was the big question when Covid landed: are allergic people more vulnerable to Covid-19 or not? More than two years after the start of the pandemic, the first answers are emerging. This is the following notably from a study in the scientific journal The Lancet Respiratory Medicine, and another from PNAS, published by the American National Academy of Sciences. If we had to summarize the answer, it would be: it depends.

Cells that barricade themselves better

That of PNAS is the most reassuring. It turns out that only about 5% of asthmatics, in this case those with severe asthma, are more likely to be severe Covid-19 patients. Others may be better equipped to deal with the disease. A real paradox that intrigued researchers. “We knew there had to be a biomechanical reason that could explain why some asthmatics seemed protected against severe Covid.“, Explains the study’s author, Camille Ehre, in Science Daily.

His team then decided to find out what it was all about. To do this, they studied the mechanisms of the respiratory system, both affected by Covid-19 and asthma. In the case of the coronavirus, it is its Spike proteins that allow it to attach to human cells via the ACE2 receptor. To protect themselves, these cells have a defense mechanism known as mucin MUC5AC. Problem: When the invasion is too large, the proteins responsible for its production are overwhelmed. The amount of MUC5AC mucin becomes insufficient and the coronavirus thrives.

In people with asthma, on the other hand, there is an overproduction of mucin MUC5AC due to the presence of interleukin 13 (IL-13), which is the mediator of allergic inflammation. Logically, thanks to this anti-Covid barrier, they are therefore better prepared to face the coronavirus. Even better, IL-13 also reduced the production of the ACE2 receptor, which further limits the chances of infection and therefore contagion to surrounding cells. In summary, the respiratory system is barricaded. Laboratory experiments with the use of IL-13 on human lung cells have confirmed this hypothesis. A path to develop new treatments against Covid-19. “This study shows the importance of some specific mechanisms, involving the expression of IL-13, and how this could be used to protect patients and prevent them from developing severe forms of Covid.“says Camille Ehre.

Some asthmatics much more vulnerable than others

However, the researcher admits that there are still gray areas on the exact mechanism of IL-13. What protects the most: MUC5AC mucin production or ACE2 receptor reduction or a mixture of both? Therefore, the use of IL-13 as a drug as such is excluded, as it would cause inflammation in people who already suffer from this problem. Finally, there are still people with asthma who react very badly to the coronavirus.

Among those particularly sensitive to Covid-19, there are at least some children. This is the subject of The Lancet study. To prove this, the researchers looked at large sizes, with a cohort of 750,000 children between the ages of 5 and 17. 5.8% of them contracted Covid and 0.9% were hospitalized. Among the 63,000 asthmatics surveyed, these rates rose to 6.8% and 1.5%, respectively. But a child with asthma is not another. Again, those with severe asthma were more likely to end up in hospital, with 548 in 100,000 cases, compared with 94 in 100,000 among other asthmatics.

This study partly explains why asthma in general has not emerged as a risk factor for severe COVID-19 in some studies, because it is a truly significant risk factor for only a fraction of asthmatics. [ceux dont la maladie n’est pas contrôlée] and not necessarily for all asthmatics“, explains Dr. Jesse Papenburg, pediatric microbiologist-infectivologist at Montreal Children’s Hospital to the Quebec newspaper Le Devoir. According to her, we must therefore remain cautious about the similar a priori number of hospitalized and non-asthmatic Covid asthmatics. Confinement may have encouraged people to protect themselves from allergens as well, which can skew the figures. The rest of the pandemic will show whether later, in the absence of quarantine, the representativeness of allergic people changes among Covid-19 patients.

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