Initial guidelines advised that sensitization to PEG should be taken into consideration in suspected subjects before a recommendation on the administration of vaccines for COVID-19 containing PEG or its cross-reactive analogues. ³ However, PEG shows an important variability in terms of molecular weights and conjugation forms. In that sense, although it is known that PEG-2000 (MW: 2000g/mol) conjugated with lipids is the form contained in the vaccines for COVID-19, there has been great variability in the PEG molecules used in allergy tests to evaluate sensitization of suspected subjects in the context of the current COVID-19 vaccination campaigns. ⁴ In this context, recent findings have shed light on the specific form of PEG that could be responsible of the hypersensitivity reactions to the mRNA vaccines for COVID-19.