Other adverse events include local site reactions (7.5 cases per 100,000 doses distributed), headaches (4.1 cases per 100,000 doses distributed), hypersensitivity reactions (3.1 cases per 100,000 doses distributed), and urticaria (hives) (2.6 cases per 100,000 doses distributed) [REF].
The FDA and the CDC monitor events to see if there are patterns, or more serious events than would be expected from chance alone [REF].