Polythylene glycol severe allergy and SARS-CoV-2 vaccines: usefulness of testing with PEG 1500 extract.

Summary
Background. Polyethylene glycol (PEG) is being used for first time as an excipient for mRNA anti-SARS-CoV-2 vaccines containing-PEG2000, highlighting it as a potential cause of anaphylaxis. Objective. To assess the usefulness of skin tests using PEG1500 extract in patients with suspected allergy to SARS-CoV-2 vaccines. Methods. We evaluated 126 patients with moderate-high risk of allergy to SARS-CoV-2 vaccines referred to our department from March-December 2021. Skin tests were performed with PEG1500 extract (Roxall), using a stepwise approach, with readings at 30 minutes: prick tests with 0.1%, 1% and 10% concentrations; if negative, intradermal tests with 0.0001%, 0.001% and 0.01% concentrations. The same protocol was applied to 5 healthy controls. Results. Six patients had positive immediate intradermal tests with PEG1500, all with severe PEG allergy: one with a near-fatal anaphylaxis after glucocorticoid injection containing-PEG3350 and five with systemic allergic reactions after mRNA vaccines containing-PEG2000 (Pfizer-BioNTech or Moderna). One patient developed anaphylaxis during intradermal test. These six patients were negative to polysorbate 80. The remaining 120 patients had negative tests to PEG1500; seven had positive tests to polysorbate 80. All controls had negative tests. Conclusions. To our knowledge this is the first study describing the allergy work-up testing with PEG1500 commercial extract in the scope of SARS-CoV-2 vaccination. The algorithm designed for skin tests revealed to be a useful tool. Severe PEG allergy was diagnosed in 5% of patients, contraindicating PEG-containing vaccines. PEG allergy was excluded in one hundred patients that afterwards took SARS-CoV-2 vaccines containing-PEG2000. Investigation should be conducted in specialized drug allergy centres.