Between December 1, 2023 and January 23, 2024, the Centers for Disease Control and Prevention (CDC) was notified of 23 confirmed U.S. cases of measles, including seven direct importations of measles by international travelers and two outbreaks with more than five cases each. Most of these cases were among children and adolescents who had not received a measles-containing vaccine (MMR or MMRV), even if age eligible.