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I have a number of patients who have had immediate "allergic" reactions to radiocontrast dye. They now want to know if they can get Pfizer or Moderna COVID-19 vaccine. 1) Do any of the radiocontrast dyes (OR gadolinium based dyes for MRIs) have PEG or Polysorbate in them that might contraindicate these m-RNA COVID-19 vaccines? I don't see these diagnostic agents on the PEG/polysorbate list of the recent JACI article on this topic but don't know if that means they don't contain PEG or polysorbate. 2) Also, does a history of tolerating oral Miralax indicate that the patient is unlikely to be sensitive to PEG or polysorbate?

Question #1 is asking if radiocontrast or MRI contrast reactions might suggest sensitivity to one of the constituents of the mRNA COVID-19 vaccines, particularly polyethylene glycol (PEG). I think it is important to emphasize that the cause of reactions to COVID-19 vaccines may not be related to macrogol intolerance or allergy. Rather that is a working hypothesis and many investigators question the relationship. However, the only contraindication stated for CDC for the liposomal mRNA vaccines by Pfizer and Moderna is a history of a systemic reaction, of any severity, to a prior dose or sensitivity to a component of the vaccine, potentially polyethylene glycol (1). It remains a possibility the reactions are due to contact with the lipid coating of the mRNA or other mechanism and are not immunologic. Macrogols such as PEG and related compounds such as polysorbate are used in multiple medications and personal care products. However, I could not find any evidence that macrogols or polysorbate are in radiocontrast or MRI contrast agents. Radiocontrast reactions are not immunologic except rarely. Thus, subjects with radiocontrast reactions is not a concern in delaying or omitting mRNA COVID-19 vaccines.

Question #2 relates to tolerance of one macrogol, Miralax™ or polyethylene glycol 3350, and the potential to react to other macrogols. Allergy to PEG is rare but occurs (2). Reactions are more common with higher molecular weight PEG (the number following “PEG” is the molecular weight in daltons for medications or is the number of 44 dalton-ethylene oxide units in cosmetics). However, the molecular weights of macrogols vary from 300 to 35 million daltons. One could not be certain that tolerance to topical use of PEG 3350 for a laxative would assure no reaction to other PEG entities injected. Nevertheless, it is reassuring. There are discussions of testing individuals to assess PEG allergy but the predictive value of such testing is unknown (2,3).

1. Interim Clinical Considerations for Use of mRNA COVID-19 Vaccines | CDC
2. Sellaturay P, Nasser S, Ewan P. Polyethylene glycol-induced systemic allergic reactions (anaphylaxis). J Allergy Clin Immunol Pract 2021;9:670-5.
3. Banerji A, Wickner PG, Seff R et al. mRNA vaccines to prevent COVID-19 disease and reported allergic reactions: current evidence and suggested approach. J Allergy Clin Immunol Pract 2021 (in press).

I hope this information is of help to you and your practice.
All my best.

Dennis K. Ledford, MD, FAAAAI
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