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In 2000, measles was declared eliminated in the U.S. by WHO definition (absence of endemic transmission for ≥12 months). This status has continued despite rising case numbers over the past few years (specifically attributable to two large, lengthy outbreaks in 2019).
CDC conducted surveillance of measles cases from January 2020 through March 2024, when 338 cases were reported (95% confirmed by rRT-PCR; 13 cases in 2020, 49 in 2021, 121 in 2022, 58 in 2023, and 97 in 2024). The vast majority of cases (96%) were related to an importation, and most (61%) occurred in U.S. residents who were unvaccinated or had unknown vaccination status. Cases were classified into 92 transmission chains (median outbreak size, 6 cases; range, 3–86 cases), 62 isol…