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Allergic Reactions To mRNA COVID-19 Vaccines Rare, Usually Mild And Treatable: Study

Allergic Reactions To mRNA COVID-19 Vaccines Rare, Usually Mild And Treatable: Study
Most allergic reactions associated with mRNA-based COVID-19 vaccines are due to PEG.

Vaccine manufacturers can also reformulate the mRNA vaccines to make them less likely to trigger allergic responses.

Written by Longjam Dineshwori |Updated : September 18, 2021 1:31 PM IST

Stating that vaccines are the most critical tool to end the pandemic, the World Health Organisation (WHO) has urged the world leaders attending the 76th session of the United Nations General Assembly (UNGA) to ensure equitable access to COVID-19 vaccines. Meanwhile, many people are not willing to get vaccinated fearing allergic reactions to COVID-19 vaccines.

There have been reports of severe allergic reactions including anaphylaxis associated with two mRNA vaccines, produced by Pfizer-BioNTech and Moderna. However, several studies have shown that such reactions occur rarely, and the benefits of COVID-19 vaccination far outweigh the risks. As estimated by the US vaccine safety monitoring system, Vaccine Adverse Event Reporting System, rates of severe vaccine-related anaphylaxis -- allergic reactions bad enough to require hospitalization -- are 4.7 and 2.5 cases per million doses for the Pfizer and Moderna vaccines, respectively.

Another study from the Stanford University School of Medicine has concluded that allergic reactions to mRNA-based COVID-19 vaccines are rare, typically mild and treatable. The authors of the study, published online in JAMA Network Open, also suggested that vaccine manufacturers can reformulate the vaccines to make them less likely to trigger allergic responses, as well as explained how.

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Causes of allergic reactions after COVID-19 vaccination

For the study, the researchers analyzed 22 potential allergic reactions reported after the first 39,000 doses of Pfizer and Moderna COVID-19 vaccines were given to health care providers at Stanford soon after the US FDA approved emergency use of the vaccines in the country.

They found that most of the patients who developed reactions were allergic to an ingredient that helps stabilize the COVID-19 vaccines, i.e. polyethylene glycol (PEG). PEG is also widely used as a stabilizer in household products, cosmetics and medications. But they did not show allergies to the vaccine components that provide immunity to the SARS-CoV-2 virus. In addition, they found that these allergic reactions occurred via an indirect activation of allergy pathways. Hence, they are easier to mitigate than many other allergic responses.

"Having an allergic reaction to these new vaccines is uncommon, and if it does happen, there's a way to manage it," said the study's senior author Kari Nadeau, as quoted by ScienceDaily. He is the Naddisy Foundation Professor in Pediatric Food Allergy, Immunology, and Asthma.

For those who have had allergic reactions to these COVID-19 vaccines, it is advisable to consult an allergist prior to the administration of additional doses. Most of them can safely receive a second dose under medical supervision, the researchers stated.

How to make mRNA vaccines less allergic

Because most reactions associated with the mRNA-based COVID-19 vaccines were due to PEG rather than the vaccine's active ingredients, the researchers suggested that vaccine manufacturers can reformulate the vaccines with different stabilizers that are less likely to cause allergies.

Allergic reactions to Pfizer and Moderna COVID-19 vaccines were generally mild and can be managed with antihistamines, fluids, corticosteroids and close observation.

Of the 22 participants who developed possible allergic reactions to the Pfizer and Moderna vaccines, 15 had physician-documented histories of prior allergic reactions, including 10 to antibiotics, nine to foods and eight to nonantibiotic medications.