Blumenthal's team documented all allergic reactions, including anaphylaxis, among employees at the health system that includes Mass General and Brigham and Women's Hospital, both in Boston. Among more than 52,800 employees surveyed after a first dose of an mRNA COVID-19 vaccine, 2% had an allergic reaction, and anaphylaxis occurred at a rate of 2.47 per 10,000 individuals. "To put this in perspective, this is largely comparable to anaphylactic reactions from common antibiotics,”...