From food allergies to asthma to dermatitis: Long Covid may be to blame

If you have suddenly found yourself dealing with a new food allergy or asthmatic bronchitis you have never seen before, the culprit could be Covid, or rather its consequences. The 'long-COVID' is that set of symptoms (the WHO lists over 200, from brain fog, to breathlessness, palpitations, fatigue, etc.) that accompany the resolution of the acute infectious episode for months or years. And it would be at least 6%, among those who have survived the acute infection, who become long-haulers, a terminology borrowed from long-haul air travel and which also describes those who are forced to cope with these 'after-effects', even disabling ones. Challenging numbers given the hundreds of millions of cases of SARS CoV-2 infection recorded worldwide since the start of the pandemic (in the US alone, long-haulers would be at least 20 million). But the long COVID story is still a work in progress, to which new pieces are being added every day. Like those derived from some recent studies that suggest that this elusive post-viral syndrome could be at the basis of the appearance of new allergies, both respiratory (asthma, allergic rhinitis, rhino-sinusitis), and food, and cutaneous (atopic dermatitis).

By comparing the inflammatory profiles of people with long COVID, with those of people perfectly recovered from the acute infection, Malika Boudries and colleagues at Harvard University (their study is published in Nature Immunology) found that SARS CoV-2 results in persistent immune dysregulation, characterised by a state of chronic inflammation, a kind of 'exhaustion' of the immune system, and altered energy metabolism. Other authors also call into question the uncontrolled activation of mast cells. And these are all 'ingredients' capable of favouring the appearance of new allergic reactions. But that's not all. These alterations would also be responsible for auto-immune pathologies and the reactivation of latent viral infections (e.g. from Epstein Barr, the infectious mononucleosis virus) or the 'reactivation' of forgotten allergic manifestations (such as asthma as a child, which disappeared in adulthood). Hypotheses and suspicions that are also found in another study, published in the Journal of Allergy and Clinical Immunology, which sifted through the electronic health records of 118 million Americans, discovering that after an episode of COVID-19, the risk of developing chronic rhinosinusitis was increased by 74%, asthma by 66% and allergic rhinitis by 27%.

On the other hand, the increased risk of reoccurrence of type 2 respiratory inflammatory diseases (allergic asthma, rhinitis, etc.) was not found in vaccinated subjects who had not been infected. In short, the anti-COVID vaccination also seems to protect against the immune system 'confusion state' induced by the virus from China. But this does not only concern the respiratory tract. Reports of increased hypersensitivity (if not outright allergic reactions) to gluten, histamine-rich foods and fermented foods are multiplying; not to mention those to ingredients in perfumes and household detergents. In short, the long COVID is essentially a dysfunction, or rather a real 'hijacking' of the immune system, a loaded weapon aimed at oneself, rather than against external pitfalls, which can give rise to a series of consequences, such as neo-allergies, respiratory and otherwise. According to the experts, it is important to keep a watchful eye on the appearance of these neo-allergies (and a privileged observatory is represented by the post-Covid centres, but also by the allergy clinics) to catch them in the bud and intervene before they do further damage. On the prevention front, apart from the vaccine, there is not much else at the moment. It would then be important to have biomarkers capable of identifying patients who, after the acute phase of the infection, are on the way to developing allergies; starting with those most at risk, i.e. with a family history of atopy and allergies.