ABSTRACT
BACKGROUND: The mechanism of action behind anaphylactic reactions to the mRNA COVID-19 vaccines remains unknown, but the excipient polyethylene glycol, PEG-2000, has been implicated. Initial recommendations were made for excipient testing with PEG-3350 to help risk stratify individuals and identify an etiology. Here we present a case of a patient with a history of polyethylene glycol anaphylaxis and positive skin testing to PEG-3350, who successfully received both doses of the Pfizer-BioNTech COVID-19 mRNA vaccine in a single step with only premedication. CASE PRESENTATION: A 56-year-old man was referred to our clinic for assessment of his eligibility in receiving the COVID-19 vaccine given a history of anaphylaxis to PEG. He had two anaphylactic episodes: one in 2018 to methylprednisolone acetate intra-articular injection and one to oral PEG-3350 in 2020. Confirmatory skin prick testing was done in our clinic to PEG-3350 that was positive at 35 mm with appropriate positive and negative controls. Despite this he wanted to receive the PEG-containing mRNA COVID-19 vaccines and was counselled on the risks and benefits. He successfully received both doses of the Pfizer-BioNTech COVID-19 mRNA vaccine in a single step with only pre-treatment with Cetirizine 20 mg daily and Montelukast 10 mg daily for 5 days. CONCLUSIONS: In conclusion, our case demonstrates that a patient with a confirmed polyethylene glycol anaphylaxis could safely receive both doses of the COVID-19 mRNA vaccines in a single step with pre-treatment. We hope that our case will further support the limited role in skin testing to PEG in the assessment of COVID-19 mRNA vaccine allergy and highlight the need for further research to elucidate the mechanism of action behind these allergic reactions.