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Allergists Can Safely Supervise mRNA COVID-19 Vaccination in Some PEG-allergic Patients

AAAAI News Release

December 20, 2021

April Presnell, Media & Member Communications Manager
(414) 272-6071

While skin testing to the vaccine does not predict allergic reactions to vaccines in PEG-allergic patients, some PEG-allergic patients can be inoculated with an mRNA COVID-19 vaccine when done under the supervision of an allergist, according to a new study published in an official journal of the AAAAI.

Milwaukee, WI – A case series published in The Journal of Allergy and Clinical Immunology: In Practice (JACI: In Practice), an official journal of the American Academy of Allergy, Asthma & Immunology (AAAAI), indicates that some patients with polyethylene glycol (PEG) allergies can be safely administered mRNA COVID-19 vaccines when supervised by an allergist, after a discussion of the risks and benefits.

A group of allergists across the Quebec province in Canada were designated by the Association of Allergists and Immunologists of Quebec to evaluate and vaccinate patients with allergic-like reactions to COVID-19 vaccines or a history of PEG allergy. Since the vaccination campaign in Quebec began, 12 total cases of confirmed or very likely PEG allergy have been evaluated. After a discussion of the risks and benefits, patients were offered vaccination with one of the three currently available vaccines: either an mRNA vaccine (Pfizer-BioNTech or Moderna) or the AstraZeneca COVID-19 vaccine (this vaccine is not currently approved in the United States, but it was approved in Canada). Ten patients chose an mRNA vaccine and two chose the AstraZeneca vaccine. The AstraZeneca vaccine does not contain PEG though it does contain polysorbate 80, which may be cross-reactive with PEG in some patients. Since May 13, 2021, it is no longer being offered to the general population in Quebec due to safety concerns from rare cases of vaccine-induced thrombotic thrombocytopenia. Patients vaccinated with AstraZeneca as a first dose were able to receive an mRNA vaccine for their second dose.

Six patients had a confirmed PEG allergy through positive skin prick tests or positive drug provocation tests, and two of these six tested positive for an intradermal test (IDT) to the Pfizer-BioNTech vaccine diluted 1:100. Six additional patients were considered very likely to have PEG allergy despite negative skin test results.

Four patients with a confirmed PEG allergy tolerated an mRNA vaccine, some in as little as one step. The other two of these patients received the AstraZeneca vaccine, one received both doses before being evaluated and one opted to receive it based on positive skin prick test and drug provocation test results to PEG before the AstraZeneca vaccine was no longer recommended due to the concerns mentioned above.

All six patients with suspected PEG allergy tolerated an mRNA vaccine in a single step. One of these six patients did suffer anaphylaxis to PEG between the first and second dose of the Moderna vaccine. While she tolerated the first dose in one step, her second dose was administered successfully without allergic reactions in five steps. Ultimately, the case series showed that skin test reactivity to the vaccine did not reliably predict allergic reactions to the COVID-19 vaccines, as patients who chose an mRNA vaccine were able to tolerate it.

The lack of allergic reaction could be explained by the molecular weight and dose of PEG contained in the vaccines being below the allergic threshold in the patients from the case series. Pfizer-BioNTech mRNA vaccines contain 0.05mg of PEG 2000 linked to a lipid, and Moderna’s vaccine is likely a similar dose. All patients in this case series except one had reactions to at least 28mg of PEG 3350. It’s also possible that some patients with a history of PEG allergy were no longer reactive to PEG at the time of vaccination.

“This case series shows that at least some patients with a rare allergy to PEG can tolerate an mRNA COVID-19 vaccine, when administered under the supervision of an allergist,” said Matthieu Picard, MD, corresponding author. “Though data is limited, we suspect the amount of PEG, its route of administration and molecular weight influence the risk of an allergic reaction. More research will help us further develop a safety profile for mRNA vaccines in PEG-allergic patients.”

The AAAAI’s Find an Allergist/Immunologist service is a trusted resource to help you find a specialist close to home.

You can learn more about COVID-19 on the American Academy of Allergy, Asthma & Immunology website,

The American Academy of Allergy, Asthma & Immunology (AAAAI) represents allergists, asthma specialists, clinical immunologists, allied health professionals and others with a special interest in the research and treatment of allergic and immunologic diseases. Established in 1943, the AAAAI has more than 7,100 members in the United States, Canada and 72 other countries.