Matthew S. Krantz, MD; Jason H. Kwah, MD, MSCI; Cosby A. Stone Jr, MD, MPH Allergic reactions after messenger RNA (mRNA) COVID-19 vaccines have been reported to be as high as 2%, with anaphylaxis occurring in up to 2.5 per 10 000 individuals. There is uncertainty as to whether to administer a second dose of mRNA...