A booster dose of Moderna’s COVID-19 vaccine (mRNA-1273) likely triggered a dangerous immune response in a patient with systemic mastocytosis (SM), leading to severe mast cell activation, high fevers, rash, vomiting and systemic inflammation, according to a case report published recently in Inflammation Research.
This case study highlights how certain vaccines can, in rare cases, cause major metabolic, lipid and cytokine disturbances in people with mast cell disorders — and how quick intervention may be life-saving when this occurs.
Though “the European and American mastocytosis societies recommended mRNA-based SARS-CoV-2 vaccinations for all mastocytosis patients over 16 years of age,” they have done so “with certain precautions such as prolonged supervision after vaccination and pre-medication with histamine 1 and 2 receptor antagonists,” noted the case study’s authors.
The case describes a 43-year-old man with indolent SM. Within 24 hours of vaccination, the patient experienced escalating symptoms that met criteria for systemic inflammatory response syndrome, including a fever and a rapid heart rate of 133 beats per minute. Blood tests revealed a 26% drop in platelet count, severe elevation in tryptase (a mast cell marker) and a peak histamine level of 18 ng/ml, which is considered life-threatening.
The patient was treated with antihistamines and tocilizumab, a drug that blocks interleukin-6 (IL-6), a key inflammatory molecule. Clinical symptoms began to improve within 12 hours of treatment.
Read more about SM causes and risk factors
Over a year later, the same patient had another mast cell activation event following a confirmed COVID-19 infection. Although symptoms were less severe, IL-6 was again elevated and tocilizumab was used with good effect.
“Since IL-6 is consistently highly elevated during MCA [mast cell activation] events in this patient, the anti-IL-6 receptor antibody tocilizumab was administered in both events,” explained the authors of this report. “Considering the pro-inflammatory role of IL-6, the strong positive correlation between IL-6 concentrations and mortality, and the adverse event profile of tocilizumab in thousands of rheumatoid arthritis patients likely treated multiple times, single administration of tocilizumab during severe MCA events is justified.”
This repeat episode strengthens the link between virus exposure and mast cell activation in patients with SM. The authors noted that lab experiments on mast cell lines exposed to both Moderna and Pfizer mRNA vaccines showed variable and inconclusive effects, but that cell damage was consistently observed.
While the benefits of COVID-19 vaccination still outweigh the risks for most, this case underlines the importance of tailored care for individuals with mast cell diseases. For patients with SM, clinicians may consider preemptive strategies or emergency planning around vaccination to reduce potential harm.
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