Florida Measles Outbreaks Could Become A Fixture For Decades, Model Projects

Measles does not need one giant epidemic to settle in for good. Smaller waves that keep returning can do the job just as well, and that is the pattern a new mathematical model projects for Florida. Florida announced plans in September 2025 to remove its vaccine mandates, including the school requirement for the measles, mumps, and rubella (MMR) shot, and the simulations show what could follow in a state where the model says coverage already falls short.

Published in Proceedings of the National Academy of Sciences, researchers at the University of Maryland built the model to test what dropping the school MMR requirement could mean. In their worst-case scenario, MMR uptake among incoming children falls to 82%, and a pronounced outbreak arrives within three to five years. Smaller waves follow, arriving more often, and the simulations kept them going for decades. Even at the 88% coverage recorded for 2024 and 2025, outbreaks persisted.

Florida is starting from a weak position, according to the authors, who estimate that current MMR coverage already falls below the level needed to prevent sustained measles spread. Each outbreak drains the pool of unprotected people, and each new group of unvaccinated kids refills it. Some of those children stay unprotected as they grow into adults, which keeps the pool from ever emptying out.

Florida measles outbreaks start from a low baseline

Measles ranks among the most contagious infections known. One case in a group with no protection is estimated to spark 12 to 18 more, and the authors describe measles control as sensitive to small drops in vaccination, “reflecting the narrow margin of safety between control and disease resurgence.”

Recent national numbers show what a thin margin looks like. CDC data show 2,144 measles cases nationwide in 2025, a 650% jump from 285 in 2024, with major outbreaks in Texas, New Mexico, and South Carolina.

Earlier studies put the vaccination level needed to stop sustained spread, known as the vaccine-induced herd immunity threshold, at 91 to 98% for the United States, depending on assumptions about how people mix and how well the shot works. Florida’s kindergarten MMR coverage averaged 91.6% from 2011 to 2025, and the model assumed adult coverage of 92.5% from the same CDC data. Those levels sit below the threshold the model calculated for Florida.

Recent classes look worse than that average. Kindergarten coverage has stayed between 88 and 90% over the past three school years, and the authors write that continued declines “could move the state even farther below the threshold required for sustained elimination.”

Building the model from a Texas outbreak

Alice Oveson and Abba Gumel split Florida’s population into two groups, about 4.1 million children and about 18.9 million adults, and tracked how many people in each group were unprotected, vaccinated, exposed, contagious, or recovered. Spread was calibrated against case counts from the 2025 outbreak in Gaines County, Texas, while contact patterns came from published data on urban American life. Children matter most in those patterns, since they have “far more close interactions than adults,” in the paper’s words. Vaccine effectiveness was fixed at 97% in the main simulations.

A repeal scenario required a guess about how far coverage might fall. Authors turned to a national survey of parents in which about 16% were “not confident” that the MMR vaccine is safe for children, 17% believed “the risks of the MMR vaccine outweigh its benefits,” and 18% opposed school-entry requirements for the shot. From there, they estimated that removing the requirement could cut coverage among incoming children by up to 18%, to as low as 82%. Coverage of 90% served as the best case, so the simulations ran from 82 to 90%. That 82% figure is an assumption built from survey opinions, not something observed after a repeal.

Smaller Florida measles outbreaks, arriving more often

Early on, the numbers looked dramatic. At child coverage of 82 to 86%, simulated peaks topped those of any year in the United States since 1977, reaching an estimated 260 to 315 cases per 100,000 children at the height of the wave. Adults saw about half that, from 135 to 160 cases per 100,000.

Long-run simulations, covering 2030 to 2080, told a different story. Outbreaks in all age groups got smaller but came more often, which the authors say may be driven by lower childhood vaccination expanding the pool of unvaccinated children. With no other interventions and coverage at 82%, that pattern of persistent, more frequent waves emerged within roughly a decade. At the 88% baseline, later waves arrived later and peaked lower, but they persisted. A similar trend appeared even when uptake rose to 90%.

Authors write that “simulations suggest that Florida will continue to experience measles outbreaks over the next 50 years,” and that “measles will potentially become endemic in Florida,” meaning a permanent presence. A condition comes attached: the waves persist “unless the current vaccination coverage is increased” or childhood vaccination is paired with adult catch-up shots or other measures. Repeated outbreaks also produced measles deaths in the simulations, and the paper’s summary statement says repeal could bring projected child deaths “numbering in the hundreds” within five years.

Catch-up shots and masks slow Florida measles outbreaks, but only so far

Two stopgaps were tested on top of the base model: isolation after the rash appears, and masks for children once cases emerge. At 88% coverage, the authors report, short-term isolation and masking can shrink an epidemic considerably. In the 82% scenario without isolation, masking with compliance above 80% cut illness and deaths by 85%, though masking alone might not prevent outbreaks. Isolation works well on paper, but many families would struggle to take time off work or arrange child care, as the paper acknowledges.

Both measures share a limit. They act during outbreaks and do nothing about unvaccinated children piling up in between. Authors write that these tools “cannot substitute for the sustained immunity provided by vaccination mandates,” a policy position that goes beyond what the math alone can show.

Vaccinating adults could offset part of the gap, but not cheaply. Per dose, vaccinating one child cut outbreak potential more than three times as much as vaccinating one adult. If child coverage stayed near 91%, raising adult coverage by 4 to 5%, to about 96.5%, would push Florida above its herd immunity threshold, which works out to roughly 900,000 additional vaccinated adults. Authors say they are “not aware of any efforts being made to vaccinate adults against measles in Florida.” Once child coverage slips below about 89%, the model says adult shots alone cannot close the gap at all, a level close to where recent kindergarten classes have landed.

Measles settling into Florida for good would not take one catastrophic year. In the model, it takes a steady stream of unprotected kindergartners, class after class, until outbreaks become routine. Even 90% coverage, at the top of recent years’ range, did not stop the waves in the simulations, which leaves the authors arguing that coverage has to rise, not fall, for the pattern to break.

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Disclaimer: This article reports results from a mathematical modeling study. The figures are projections that depend on the authors’ assumptions (including a worst-case vaccination rate of 82% derived from national survey responses), not observed events or forecasts of what will happen. The model was calibrated on one outbreak in Texas and divides the population into only two age groups. It cannot establish that any policy change will cause a particular outcome. This article is for general information and is not medical advice. Readers with questions about MMR vaccination should talk with a health care provider.

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