MMR Vaccination Rates Decline Across 2,066 US Counties Amid Measles Rise

A comprehensive county-level analysis by Johns Hopkins University researchers has revealed a nationwide decline in measles-mumps-rubella (MMR) vaccination rates across the U.S. among children since the COVID-19 pandemic began. The study found that 78% of 2,066 counties in 33 states experienced decreases in vaccination coverage, with the average county-level rate dropping from 93.92% to 91.26%, moving further away from the 95% herd immunity threshold needed to prevent measles outbreaks. Only four states—California, Connecticut, Maine, and New York—reported increases in median county-level vaccination rates. This decline is particularly concerning given the resurgence of measles cases, with over 1,000 confirmed cases reported in 2025, the most in over three decades, predominantly among unvaccinated children. The granular county-level data highlights significant heterogeneity within states, indicating that state averages can mask vulnerable pockets with substantially lower vaccination rates, underscoring the need for targeted public health interventions at the local level. Lauren Gardner, senior author and director of Johns Hopkins University's Center for Systems Science and Engineering, emphasized that understanding this detailed vaccination landscape is critical for anticipating and preventing measles outbreaks.