In 2000, measles was declared no longer endemic in the U.S. following eradication campaigns that began in 1967. Although declared eliminated, measles importations continued to occur.

During January 1, 2020–March 28, 2024, a total of 338 U.S. measles cases were reported; 29% of these cases occurred during the first quarter of 2024, almost all in persons who were unvaccinated or whose vaccination status was unknown. Prolonged outbreaks have threatened the U.S. measles elimination status.