Researchers in the UK have linked anaphylaxis in a patient who received the Pfizer-BioNTech COVID-19 vaccine with her allergy to polyethylene glycol (PEG), which stabilizes lipid nanoparticles that deliver mRNA in the vaccine to cells in the body.
Although anaphylaxis after receiving an mRNA vaccine is rare, the woman had required adrenaline after a previous severe systemic allergic reaction to azithromycin that contained PEG. Her systemic reactions to consumer products like shampoo, toothpaste, and mouthwash containing PEG were less severe.
Suspecting that an undiagnosed PEG allergy had caused her reactions, the researchers performed skin prick testing. The woman developed a systemic reaction to a 1% concentration of PEG 4000 that required treatment with adrenaline, chlorphenamine, and hydrocortisone.
Allergies to PEG, which is often found in some medications and personal care products, are rare. The authors suggested that prior to COVID-19 vaccination, clinicians use a previously published algorithm for skin prick testing to screen patients for PEG allergy without provoking a severe reaction in those who are allergic.
“In a patient with a suspected or proven PEG allergy, mRNA vaccines containing PEG should be avoided,” the authors wrote. However, they emphasized that PEG allergy and anaphylaxis following COVID-19 vaccination are rare and that the vaccines are safe.