Background: Allergic reactions have been reported to occur after vaccination with both the Pfizer-BioNTech COVID-19 Vaccine and Moderna COVID-19 Vaccine. Allergic reactions range from mild to severe and include life-threatening anaphylactic reactions, although no deaths have been reported with either vaccine.

This study is designed with two principal aims:

To estimate the proportions of systemic allergic reactions to the Pfizer-BioNTech COVID-19 Vaccine and the Moderna COVID-19 Vaccine in a High-Allergy/Mast Cell Disorder (HA/MCD) population, and

If the risk in the HA/MCD is demonstrable, determine whether the proportions are higher in the HA/MCD compared to a non-atopic population.