A new study reports that coronavirus disease 2019 (COVID-19) vaccinations are generally safe and effective in patients with systemic mastocytosis (SM) and other mast cell activation disorders. However, the study, published in Allergy, observed an increase in hypersensitivity and anaphylactic reactions in these patients.

“The reports of anaphylaxis are of concern for patients with mast cell activation disorders and have created vaccine hesitancy,” the authors wrote. “The aim of this report is to provide outcomes of the safety and tolerability of COVID-19 vaccination in a large, international cohort of patients with mast cell disorders.”

The research team conducted a retrospective study of 323 patients with clonal or nonclonal symptomatic mast cell disorders who together received 666 vaccinations across 3 institutions in the United States and Europe. Adverse effects were defined as symptoms occurring within 2 hours of vaccination.

Overall, the vaccinations were well tolerated, and adverse events occurred in 6% of patients, compared to 2% in the general population. Most of the reactions were mild, such as pruritus, urticaria, flushing, and gastrointestinal symptoms, and did not require hospitalization or medical intervention.

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Six patients had reactions involving more than 1 organ. One patient had anaphylaxis according to Brighton level 1 criteria, and 5 patients met Brighton level 3/4 criteria. Two patients were treated with epinephrine. Most patients were taking antihistamines at the time of vaccination, which did not increase their risk of adverse reactions. There was no difference in the rate of adverse events between vaccine types (eg, Pfizer vs Moderna).

Due to the increase in adverse reactions among patients with SM, the authors recommend that they carry epinephrine autoinjectors with them when being vaccinated and that they schedule their vaccination at a center that can respond appropriately to anaphylactic reactions if needed.


Giannetti MP, Olivieri F, Godwin G, et al. Outcomes of Covid19 vaccination in 323 patients with clonal and non-clonal mast cell activation disorders. Allergy. Published online August 13, 2022. doi:10.1111/all.15476