Allergic reactions to messenger RNA vaccines have been recorded but these would remain rare, generally mild and easily treated.
- Allergic reactions after the first dose of mRNA vaccine are believed to be due to the stabilizer contained in the product.
- In a study, scientists give solutions to reformulate the vaccine in order to avoid them.
Currently, 50 million people received at least one dose of vaccine against Covid-19 in France, including more than 47 million who are fully vaccinated according to the Ministry of Solidarity and Health. Most of these individuals were vaccinated with doses of Pfizer or Moderna, messenger RNA vaccines. If they are effective against Covid-19, they nevertheless have, for some, side effects like allergic reactions. But, according to a study published in the journal JAMA Network Open, these side effects would be rare, usually mild and could be easily treated. The researchers believe that they should therefore not dissuade citizens from getting vaccinated.
Shortness of breath, hives, swelling, loss of consciousness…
To achieve this result, the scientists analyzed data from around 39,000 people who had their first dose of the Pfizer (31,635 individuals) or Moderna (7,260) vaccine. Only 22 of them, including 20 women, had allergic reactions such as hives, swelling of the mouth, lips, tongue or throat, shortness of breath, chest tightness, change in blood pressure or loss of consciousness. But, very quickly, all the patients were treated and got much better. No sequelae have been recorded by scientists. On the other hand, 15 of these patients had already had allergic reactions. Of these histories, 10 people reacted badly to antibiotics, nine to food, and eight to non-antibiotic medications.
Allergies due to the stabilizer present in the vaccine
Most of the patients studied by the researchers had side effects from a component of the vaccine called a stabilizer. This allows the quality of the product to be maintained during storage. According to the authors, this stabilizer would also be present in medicines, household products or even in certain cosmetics. Thus, women would therefore be more likely to be exposed to large quantities of this substance, which could explain why they had more allergies to vaccines. Indeed, repeated exposure to a substance can sometimes sensitize the immune system and cause allergies.
Reformulating vaccines to minimize the risk of allergies
The authors point out that most allergic reactions are therefore not due to the ingredients of the vaccine that protect against the virus, which seems reassuring to them. In addition, these adverse effects occurred through indirect activation of allergic pathways, making them easier to treat. “Good to know these reactions are manageableexplains Kari Nadeau, one of the authors. Having an allergic reaction to these new vaccines is rare, and if it does happen, there is a way to manage it.. (…) It does not appear that mRNA itself causes allergic reactions.” In their study, the scientists also offer solutions to laboratories to reformulate vaccines so that they trigger – even – fewer allergic reactions. According to the US vaccine safety program, the most severe manifestations of allergies (which require hospitalization) represent only 4.7 cases out of a million doses Pfizer and 2.5 for Moderna. So very low risks for great benefits to these vaccines.
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