Washington Post When it comes to infectious diseases, measles is “the canary in the coal mine,” one expert said. There are more than 900 confirmed measles cases in the United States, as of the Centers for Disease Control and Prevention’s most recent weekly count. It’s less than two months into the year, “and we already have over a quarter of [the measles cases] we had all of 2025, so things are not great,” said Katrine Wallace, an epidemiologist and adjunct assistant professor at the University of Illinois at Chicago School of Public Health. Measles is the most contagious disease known and can be serious, especially for young children. It spreads when a person coughs or sneezes and can cause a distinctive rash with flat red spots, along with fever and upper respiratory symptoms. More severe complications sometimes develop, such as pneumonia and encephalitis. Before a vaccine was available, measles was responsible for an estimated 2.6 million deaths a year.
Two doses of the measles, mumps and rubella or measles, mumps, rubella and varicella (chickenpox) vaccines — MMR and MMRV, respectively — usually provide lifetime protection against measles. At least 95 percent of the population needs to be immune to achieve herd immunity, which is critical for protecting those who can’t be vaccinated, such as children younger than 12 months. But plunging vaccination rates allow outbreaks to occur, and even states that have vaccination rates above 90 percent are experiencing outbreaks.