On Aug. 28, 2026, America’s kindergartners are heading back to school less vaccinated than ever. New Centers for Disease Control and Prevention (CDC) data analyzed by Scientific American’s Jackie Flynn Mogensen and Sanidhya Sharma show kindergarten MMR vaccination fell to 92.4 percent this year, down from about 95 percent a decade ago, while nonmedical exemptions have roughly doubled, to 4 percent. Measles, once eliminated in the U.S., has logged over 2,500 cases this year, the most since 2000.

Idaho’s kindergarten MMR rate has dropped 15 percentage points in a decade, while Connecticut, Maine and New York have held steady or climbed, a split tied partly to which states allow personal exemptions.

Experts point to pandemic-era disruption, eroding trust and rising misinformation, including from Washington, where a recent executive order pushed to split the MMR shot into three doses. As Lori Handy of Children’s Hospital of Philadelphia’s Vaccine Education Center puts it: “The lower the vaccination rates are, the more we anticipate outbreaks.”