In 2000, thanks to an effective vaccine with high uptake, the U.S. achieved a rare public health victory: zero cases of endemic measles transmission. But measles has persisted, with repeated outbreaks over the years, and it is having a big comeback. In the U.S., 23 cases of measles were reported over less than eight weeks in December and January, including seven cases brought in by international travelers and two outbreaks each involving more than five people. There was a thirtyfold increase in measles cases in Europe in 2023, with tens of thousands of hospitalizations and five deaths.