Background: As the vaccination campaign in response to the
coronavirus disease 2019 (COVID-19) pandemic continues, concerns with regard to adverse reactions to the
vaccine remain. Although
immediate hypersensitivity reactions have received much attention, delayed systemic urticarial reactions after vaccination can occur. Objective: To describe the clinical presentation,
vaccine excipient skin testing results, and outcomes of subsequent
COVID-19 vaccination in patients who experienced delayed systemic urticarial reactions after
messenger RNA (
mRNA)
COVID-19 vaccination. Methods: This was a retrospective case series of 12 patients referred to the Mayo Clinics in Rochester, Minnesota, and Jacksonville, Florida, between January 19, 2021, and April 30, 2021, for evaluation of delayed systemic urticarial reactions after
mRNA COVID-19 vaccination. Demographics, medical and allergic history, reaction details,
vaccine excipient skin testing results (when performed), and the outcome after subsequent vaccination were collected for each patient. Results: The mean age of the patients was 52 years, all were white, and 9 (75%) were women. Half of the patients had a history of
drug allergy, and one had a history of
chronic spontaneous urticaria. Seven patients reacted to the Pfizer-BioNTech
vaccine and five reacted to the Moderna
vaccine. Seven patients developed symptoms between 8 and 24 hours after vaccination. Nine patients required
antihistamines for treatment. The median time to symptom resolution was 4 days. Nine patients underwent allergist-directed
COVID-19 vaccine excipient skin testing, all of which were negative. Ten patients chose to receive their next
mRNA COVID-19 vaccine dose, and four patients experienced recurrent delayed
urticaria. Conclusion: Delayed systemic urticarial reactions after
mRNA COVID-19 vaccination were not life-threatening, could be treated with
antihistamines, and were not predicted with
vaccine excipient skin testing. They were not a
contraindication to subsequent vaccination, although patients should be counseled with regard to the possibility of recurrence.