News headlines and stories this year have ticked off the list of locations where people have faced potential exposure to measles, with new ones regularly emerging: a public school in Florida. A day care in Philadelphia. An airport in Denver. A migrant shelter in Chicago.

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Taken together, the country's total caseload may not appear overwhelming: 45 measles cases had been reported across 17 states as of March 7, according to the Centers for Disease Control and Prevention. That put the U.S. on pace for around 245 cases by the end of the year, easily its highest total in the past five years but still a far cry from the nearly 1,300 seen in 2019, which marked the largest number of cases reported in the U.S. in roughly three decades.

Yet the threat posed by measles is insidious. The highly contagious disease can infect up to 90% of people in proximity to someone who has it if they are not immune. It can lead to complications such as pneumonia and encephalitis, and can kill between 1 and 3 children for every 1,000 infected.

Combine that contagiousness with vaccine skepticism and lagging vaccination rates, and experts say there's real cause for concern.

“We’re sitting on a powder keg,” Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota School of Public Health, says of his state. “And this is the case throughout much of the country.”

In Minnesota specifically, about 87% of kindergarteners in the 2023-2024 school year were vaccinated for measles, yet state data also points to nearly 90 schools in Hennepin and Ramsey counties – home to the Twin Cities – with kindergarten vaccination rates under 75%. Experts........

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