Speaker: Siyu Chen
Date: Friday, January 23, 2026
Time: 1:00 – 2:00pm EST
Abstract: Measles is resurging in high-income countries that previously achieved elimination, yet current surveillance relies on county-level aggregates that obscure fine-scale clustering where outbreaks originate. We assembled the nationwide multiscale vaccination database spanning 45 US states (2013–2025), encompassing over 50,000 schools, 13,000 districts, and 3,000 counties. Using a gravity-based transmission framework, we demonstrate that 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 COVID-19 pandemic. School district boundaries frequently misalign with counties, creating cross-boundary transmission corridors that can push well-vaccinated counties above epidemic threshold through spillover alone. Preventing measles re-endemicity requires surveillance systems operating at the spatial scale where vulnerability accumulates.
Bio: Siyu is an infectious disease epidemiologist and modeler at Cornell University. Her work spans scales: from within-host responses to population transmission dynamics, from local outbreaks to multi-spatial scale risk mapping. She received her doctorate from Oxford, collaborating with UK Health Security Agency on COVID-19 pandemic response evaluation in England. After a year at Princeton studying sex differences in influenza antibody responses, she joined Cornell to model measles resurgence in various settings. Her multiscale frameworks reveal how heterogeneity in vaccination coverage shapes outbreak risk, demonstrating that school-level surveillance captures transmission dynamics invisible to county-level monitoring with direct implications for US public health preparedness.