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

School-level measles transmission potential in the US became supercritical in 2022-2023, with vaccination susceptibility doubling to 10%, surpassing epidemic thresholds unnoticed by current surveillance.

• Why it matters: Understanding fine-scale susceptibility is crucial because current aggregated data mask localized outbreak risks, hindering timely interventions to prevent re-establishment of endemic transmission.
• What they did: A nationwide vaccination database covering over 50,000 schools and 13,000 districts was used to develop a transmission model, revealing shifts in epidemic risk across multiple spatial scales from 2013 to 2025.
• The result: Findings highlight that targeted surveillance and interventions at school and district levels are essential to intercept imported cases early and prevent widespread measles outbreaks in the US.