Study: COVID-19 mRNA Vaccines Rarely Cause Allergic Reactions


Stanford research results show that of nearly 39,000 individuals, just 22 had potential allergic reactions, and all recovered.

The mRNA-based COVID-19 vaccines rarely cause allergic reactions, and if they do, the reaction is typically mild and treatable, according to research results from the Stanford University School of Medicine.

“It’s nice to know these reactions are manageable,“ Kari Nadeau, MD, PhD, the Naddisy Foundation professor in Pediatric Food Allergy, Immunology, and Asthma, said in a statement. “Having an allergic reaction to these new vaccines is uncommon, and if it does happen, there’s a way to manage it.”

The allergic reactions occur because of an indirect activation of allergy pathways, which makes them easy to mitigate.

For the Moderna and Pfizer vaccines, the rates of severe vaccine-related anaphylaxis that required hospitalization were 2.5 and 4.7 cases per million of doses, respectively, according to Vaccine Adverse Event Reporting System.

This, however, does not account for all allergic reactions to the vaccines.

Investigators analyzed 22 potential allergic reactions from nearly 39,000 doses of both the Moderna (7260 doses) and Pfizer (31,635 doses) COVID-19 vaccines given to health care providers at Stanford. The study started soon after the vaccines received emergency use authorization from the FDA.

Of the 22 individuals with allergic reactions, 17 had reactions that met diagnostic criteria for an allergic reaction, and 3 received epinephrine.

All 22 individuals recovered.

Additionally, 15 individuals had history of prior allergic reactions: 10 to antibiotic medication, 9 to food, and 8 to nonantibiotic medication.

Some individuals had more than 1 reaction.

Investigators looked for symptoms starting 3 hours after the vaccination, such as changes in blood pressure; chest tightness; hives; loss of consciousness; shortness of breath; swelling of the lips, mouth, throat, or tongue; or wheezing.

The study results showed that most allergic reactions were related to an ingredient that helps stabilize the vaccines, but they did not show allergic reactions occurring because the components that improved immunity to the virus.

The mRNA-based vaccinations provide immunity through small pieces of messenger RNA for making proteins that trigger an immune response that causes the immune system to recognize and fight a virus.

The findings were published in JAMA Network Open.


Allergies to mRNA-based COVID-19 vaccines rare, generally mild, Stanford study finds. EurekAlert. News release. September 17, 2021. Accessed on September 20, 2021.

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