A U.S. health agency on Wednesday announced the launch of a study of allergic reactions to two COVID-19 vaccines. The phase two trial will examine whether people who are highly allergic or have a mast cell disorder are at increased risk for an immediate, systemic allergic reaction to the vaccines made by Moderna and Pfizer-BioNTech. A systemic allergic reaction to a vaccine means a reaction occurs in one of more parts of the body beyond the site of the injection. If such reactions occur during the study, investigators will assess whether they are more frequent in participants who have a history of allergies or have mast cell disorder, versus other trial participants. Investigators will also probe the biological mechanism behind the reactions and try to pinpoint whether genetic patterns or other factors could predict which people are most at risk. The trial is being funded and sponsored by the National Institute of …