County, district and community-level measles transmission in the United States in 2013-2025.

Abstract

The United States declared measles eliminated in 2000. In 2025-2026, more than 3,500 cases have placed that status under formal review. Vaccine hesitancy, accelerated by COVID-19 disruption and misinformation, has eroded the immunological buffers sustaining elimination. Current surveillance compounds this threat: county-level vaccination aggregates structurally obscure the fine-scale susceptibility clustering where outbreaks originate. We assembled a nationwide multiscale vaccination database spanning 45 US states and Washington, DC (2013-2025), encompassing over 50,000 schools, 13,000 districts and 3,000 counties, and developed a transmission model to quantify epidemic risk across different spatial scales. School-level effective reproduction numbers crossed the epidemic threshold in 2022-2023, a transition invisible to aggregated surveillance. Average susceptibility doubled from approximately 5% to 10% following the pandemic. We also show that county boundary misalignment creates cross-boundary corridors that push well-vaccinated counties above threshold through spillover from less-vaccinated populations. State trajectories diverge markedly, shaped by exemption policies and vaccination infrastructure. The spatial architecture of US measles vulnerability has fundamentally shifted: transmission potential is supercritical in schools but invisible at the scale monitored by surveillance. Preventing measles re-endemicity requires surveillance and interventions operating at school and district levels, where imported cases can be intercepted before igniting sustained transmission.