Purpose of reviewWhereas the COVID-19 pandemic has changed our lives worldwide, we hope that vaccination can combat the disease. We propose how to evaluate suspected severe allergic reactions to the vaccines so that as many as possible may be safely vaccinated. Recent findingsRare cases of severe allergic reactions after COVID-19 vaccination have been observed, seemingly at a higher frequency than for other vaccines. Few excipients are likely to have caused these reactions. IgEmediated reactions to polyethylene glycol (PEG) and its derivatives are the most suspected, albeit hitherto unproven, causes. We suggest to make a diagnosis based on skin tests with PEG and PEG derivatives and that these be considered in relation to the decisions required before the first and the second vaccine dose. A vaccine without these excipients is available, but published data about its side effects are limited.

To the Editor, Allergic reactions, including anaphylaxis, have been reported from the second day of Pfizer-BioNTech's COVID-19 vaccine administration in the mass vaccination programme. 1 Although the cause of these rare allergic reactions remains unclear, the excipient, polyethylene glycol (PEG), has been considered the culprit allergen. It is used as a stabilizer in the COVID-19 mRNA vaccines from Pfizer-BioNTech, 'Comirnaty', and Moderna, 'Spikevax'. A PEG-derivative polysorbate 80 is used in the adenovirus vector Oxford/AstraZeneca vaccine, 'Vaxzevria'. 2,3 Our aim was to present our experiences of evaluating 27 patients with systemic acute reactions to the first dose of COVID-19 vaccine plus 10 patients with suspected PEG allergy diagnosed before administration of the first vaccine dose. Our results indicate that a systemic acute reaction to the first dose, or to PEG or PEG derivatives, does not necessarily contraindicate a second dose of COVID-19 vaccine. 4,5 Thirty-seven patients were referred to, and evaluated at, the Allergy Center in Linköping, Sweden. The study was approved by the Swedish Ethical Review Authority, Dnr 2021-01301. Seven patients had an acute onset systemic reaction to the first dose of COVID-19 vaccine from Oxford/AstraZeneca, Vaxzevria, one to Spikevax (Moderna) and nineteen after the Pfizer-BioNTech vaccine, Comirnaty.