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Worried about allergic reactions to COVID vaccines? A new study finds that systemic reactions after mRNA COVID shots occurred only in people with a history of severe allergies or mast cell disorders — but the difference wasn't statistically significant. Strikingly, some of those same patients also reacted to a saline placebo, and lab tests found no clear allergic or immune mechanism at play.
A new randomized trial published in The Journal of Allergy and Clinical Immunology set out to answer a pressing question: do people with severe allergy or mast cell disorder histories face a higher risk of reacting to mRNA COVID vaccines? The short answer — sort of, but not in the way you might expect.
All systemic reactions within 90 minutes of vaccination occurred exclusively in participants with a history of severe allergic reactions and/or mast cell disorders (PSAR/MCD). However, the difference compared to those without such histories wasn't statistically significant. Even more notable: two participants in the high-risk group had severe reactions after receiving a saline placebo — and extensive lab testing found no evidence of a true allergic or immune mechanism in any of the reactors.
By the Numbers:
Why it matters: These findings suggest that reactions in high-risk patients may not be truly allergic in origin, which could reshape how clinicians counsel and monitor patients with allergy histories ahead of vaccination.
