Projected effects of removing school-entry vaccination requirements on measles transmission in Florida.

Florida's proposal to remove vaccine mandates in the state raises urgent questions about the state's vulnerability to measles resurgence. We develop and analyze an age-structured measles transmission model with heterogeneous contact patterns between children and adults, calibrated using data from the 2025 measles outbreak in Gaines County, Texas, and applied to Florida using state-specific demographic structure and measles-mumps-rubella (MMR) vaccination coverage. Using Florida-specific mixing patterns and demographic composition, we estimate the state's vaccine-induced herd immunity threshold and find that current MMR coverage already falls below the level required to prevent sustained measles transmission. Simulated declines in MMR vaccination coverage following removal of school-entry requirements further increase outbreak potential, producing epidemic sizes not seen since prevaccine eras and projecting a significant number of pediatric deaths within five years. Sensitivity analyses highlight that small reductions in child vaccination rates yield disproportionately large increases in outbreak magnitude, especially under strong assortative mixing among children. These findings indicate that Florida's vaccination policies are approaching a critical tipping point: Maintaining or improving MMR vaccination coverage is essential to prevent measles from reestablishing endemic circulation within the state and potentially spreading to the broader United States.