Two residents of Pennsylvania recently became the first US measles deaths this year. Both were unvaccinated, and one was an infant. In Lancaster County, where they lived, the share of children receiving the measles, mumps, rubella (MMR) vaccine fell from 95.5 percent in 2017 to 87.6 percent last year, well below the herd immunity threshold of 95 percent. We see this same trend playing out across the country, where the number of states with at least 95 percent of kindergarteners vaccinated for MMR has dropped from 20 in 2019 to 10 in 2025. In 24 states, the vaccine exemption rate, which includes medical and non-medical reasons, has surpassed five percent, meaning that even universal vaccination among all non-exempt kids would not be sufficient to achieve herd immunity. Under these conditions, which have resulted in over 2,000 confirmed measles cases for the second year in a row, experts predict we will lose our measles elimination status when it is reevaluated in November. One of the most frustrating aspects of this is that vaccines remain broadly popular with the American public, but it only takes about five percent of parents opting out of routine vaccinations to cause a public health problem for everyone, especially infants too young to be vaccinated.