A new study shows that even when people report a history of severe allergic reactions to medications, vaccines or allergens, nearly all of them can be fully vaccinated. The research involved close to 53,000 employees with the Mass General Brigham health care system. ... A high-risk allergy history was associated with a 2.5-times increased risk of allergic reactions, with the highest risks for hives and swelling. However, despite these symptoms, 97.6% of the employees in the study received two doses of an mRNA COVID-19 vaccine.