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Measles is a highly contagious virus with a primary case reproduction number (i.e., the average number of secondary cases per case patient) of 12 to 18. It is currently spreading rapidly owing to reduced measles vaccination coverage, which is due primarily to the disruption of local immunization programs by the coronavirus disease 2019 (Covid-19) pandemic and of growing vaccine hesitancy.1 Since 2024, all World Health Organization (WHO) regions have reported increased numbers of measles cases, with 395,521 laboratory-confirmed measles cases reported in 2024 and 16,147 reported during the first 2 months of 2025.2 Patients in more than half the reported cases were hospitalized, so the true number is probably much higher.3
This review covers clinical presentations and complications of measles, current recommendations, and the epidemiologic background of measles. It also addresses the current debates on immunization and the treatment of measles and presents information on the origins of the various measles vaccines and updates on measles diagnostic testing and molecular genotypes.
Most measles cases in the U.S. result from international travel. Make sure you and your loved ones are protected against measles before international travel.
