Patients with clonal mast cell disorders such as systemic mastocytosis (SM) may safely receive COVID-19 vaccinations in either a hospital or ambulatory setting following premedication to prevent mast cell activation, according to a new study published in Vaccines.

Conflicting evidence regarding immunoglobulin E (IgE)-mediated anaphylaxis or hypersensitivity directed against polyethylene glycol/polysorbate and tromethamine, components of the COVID-19 vaccines, complicate informed decision-making regarding the safety of COVID-19 vaccination for patients with SM or other mast cell disorders.

To determine the safety of COVID vaccinations in this patient population, researchers conducted an ambidirectional cohort study analyzing the responses of 30 patients diagnosed with clonal mast cell disorders to the vaccines. Prospective patients (n=26) underwent a prophylactic premedication protocol, while retrospective patients (n=4) did not premedicate prior to vaccination.

Premedicated patients received montelukast twice (24 hours and 1 hour) prior to vaccination. Additionally, 1 hour prior to vaccination, they received either bilastine, ebastine, or rupatadine (H1-antihistamine) and famotidine (H2-antihistamine).

One-third of patients reported a history of anaphylaxis with only 1 reporting an anaphylactic episode triggered by vaccination. Patients presented with various mast cell disorders, including cutaneous mastocytosis, indolent SM, smoldering SM, SM with associated hematologic neoplasm, bone marrow mastocytosis, and monoclonal mast cell activation syndrome.

Read more about SM subtypes

Prior to vaccination, patients underwent blood tests for complete blood cell count, routine biochemistry, and total and specific serum IgE levels as well as skin prick and intradermal testing to evaluate skin reactions to different COVID-19 vaccine components when warranted.

The 26 premedicated patients received 73 COVID-19 vaccine doses either in hospitals or ambulatory vaccination centers, while patients who were not premedicated received 8 doses in ambulatory vaccination centers. Most patients received the Pfizer vaccine, except 1 patient who received the Pfizer vaccine plus 2 Moderna vaccines.

None of the patients in either group reported mast cell activation symptoms following any of the COVID vaccinations.

“While clonal [mast cell] activation disorders are associated with increased hypersensitivity reactions that should prompt adequate monitoring at the time of vaccination, there is no evidence that IgE-mediated sensitization to excipients in this patient population is more frequent when compared to the general population,” the authors concluded.

“While it might be plausible, it is still unclear whether the absence of reactions resulted from our premedication protocol.


Rama TA, Miranda J, Silva D, et al. COVID-19 vaccination is safe among mast cell disorder patients, under adequate premedication. Vaccines (Basel). 2022;10(5):718. doi:10.3390/vaccines10050718