Few Allergic and Anaphylactic Reactions Found to mRNA COVID-19 Vaccines

According to new research from the Stanford University School of Medicine published on September 17, 2021, allergic reactions to mRNA-based COVID-19 vaccines are rare, typically mild, and treatable.

In this case series of 22 patients published by the JAMA Network with suspected vaccine allergy receiving clinical skin prick testing (SPT) and basophil activation testing (BAT) to the whole vaccine and key components (i.e., polyethylene glycol [PEG] and polysorbate 80), none exhibited immunoglobulin E–mediated allergy to components via SPT.

However, most had positive BAT results to PEG, and all had positive BAT results to their administered mRNA vaccine, with no patient sample having detectable PEG IgE.

In this study, women and those with a previous history of allergic reactions appeared to have a higher risk of developing mRNA vaccine allergy.

SPT and BAT results to whole vaccine and PEG suggest a non–IgE-mediated immune response to PEG may be responsible.

“It’s nice to know these reactions are manageable,” stated Kari Nadeau, MD.., Ph.D., who directs the Sean N. Parker Center for Allergy and Asthma Research at Stanford.

“Having an allergic reaction to these new vaccines is uncommon, and if it does happen, there’s a way to manage it.” 

In the future, these Stanford researchers say testing at baseline and longitudinal measurement of IgG PEG, BATs, and other molecules will be important to test mechanisms further.

If confirmed by more systematic future investigations, these findings highlight potential opportunities for patient risk stratification and alternatives in vaccine manufacturing. Furthermore, they can inform ongoing mRNA vaccine development, including possible COVID-19 booster shots to protect against emerging disease variants.

This study was supported by grants from the Asthma and Allergic Diseases Cooperative Research Centers, the National Institutes of Health, the National Institute of Allergy and Infectious Disease SARS Vaccine study, the Parker Foundation, and the Crown and the Sunshine Foundation. In addition, researcher industry relationships were disclosed.