Social Determinants and Outbreak Dynamics of the 2025 Measles Epidemic in Mexico: A Nationwide Analysis of Linked Surveillance Data

Measles resurgence threatens elimination achievements in the Americas. We conducted a nationwide analysis of Mexico's 2025 measles outbreak, integrating individual-level surveillance data from the Special Surveillance System for Febrile Exanthematous Dis-eases with municipal-level social determinants from eight national databases, comple-mented by molecular surveillance data. We analyzed 6151 confirmed cases (epidemio-logical weeks 8–52, 2025) using spatial autocorrelation (Moran’s I, LISA), effective re-production number estimation, negative binomial regression, and logistic regression for risk factors. Cases concentrated in Chihuahua (73%), with 45 LISA hot-spot municipalities containing 71.68% of cases. Molecular surveillance confirmed two independent intro-ductions: D8/MVs/Ontario.CAN/47.24 (98.1%) linked to the Canadian outbreak, and B3 (1.9%) in Oaxaca. Transmission followed a three-stage pattern: introduction through seasonal agricultural worker networks, amplification in undervaccinated communities, and diffusion to marginalized indigenous populations. Vaccine effectiveness was 98.2%, with 83.4% of cases in pockets of susceptibles (municipalities with ≥80% unvaccinated). Risk factors for complications included age < 5 years (aOR 3.59), indigenous status (aOR 2.35), and unvaccinated status (aOR 2.03). Indigenous individuals comprised 30% of cases but 76% of deaths. This outbreak demonstrates that national vaccination thresholds are insufficient when marginalized populations remain systematically underserved.