Florida’s Measles Risk Is Already Past Herd Immunity

A University of Maryland measles model, published September 28, 2026, finds Florida already below the coverage needed to stop sustained spread. Repealing the school MMR rule would make children the main fuse, the authors say, because one vaccinated child blocks three times more transmission than one vaccinated adult.

The Centers for Disease Control and Prevention has already counted 3,659 confirmed measles cases in the United States as of September 24, 2026, more than in any full year since 1991. Florida logged 148 of them. The school shot rule the model tests is still on the books. Coverage has slipped anyway.

Florida Kindergarten Coverage Already Misses the 95% Target

Measles was declared eliminated in the United States in 2000. It spreads in the air, and it needs very high two-dose MMR coverage to stay boxed in. The federal Healthy People 2030 target is 95%. Florida’s latest kindergarten figure is not close.

CDC school data for the 2025-26 year put Florida MMR coverage at 88.9%. The same files put 92.4% of U.S. kindergarteners up to date on MMR. Florida’s exemption rate, cited by the Maryland team, is 5.9%, against a national 4.2%.

KINDERGARTEN MMR, 2025-26

Alice Oveson, a Ph.D. student in applied mathematics at Maryland and the paper’s first author, and Abba Gumel, a Distinguished University Professor of Mathematics there, built an age-structured model with Florida’s mix of ages and contacts. They calibrated it on the 2025 measles outbreak in Gaines County, Texas. Even with the school mandate left in place, they found Florida’s vaccine-induced herd immunity already below the line that stops sustained spread.

Nationally, about 280,000 kindergarteners still unprotected against measles sat in U.S. classrooms in 2025-26, and 39 states had MMR coverage below 95%. Florida is one of them. Johns Hopkins’ International Vaccine Access Center, drawing on the same school files, shows Florida kindergarten MMR slipping from 92% in 2021-22 to 89% in 2025-26, rounded.

One Vaccinated Child Blocks Three Times More Spread

The load-bearing result is not a single Florida case count. It is who actually moves the virus. Oveson found that vaccinating one child is three times more effective at reducing transmission than vaccinating one adult. Kids spend more time face to face. Schools pack that contact into rooms, buses, and cafeterias.

Small reductions in child vaccination rates can lead to disproportionately large increases in the scale of outbreaks.

Alice Oveson, Ph.D. student in applied mathematics, University of Maryland

She likened a large unvaccinated child population to dry forest stacked with kindling. Adult catch-up shots still help. They do not replace the child dose, because adults do not mix the way classrooms do. CDC’s 2026 case file already leans young: 1,577 people ages 5 to 19, or 43% of cases, plus 656 children under 5, or 18%.

Among the 3,659 confirmed cases, 95% were unvaccinated or had unknown status. Only 3% had two MMR doses. Hospitalizations reached 327 people, or 9% of cases, including 91 of the 656 children under 5.

The Paper Projects Hundreds of Child Deaths

The Proceedings of the National Academy of Sciences summary is blunt about scale. Repealing the mandate, the authors write, could trigger the largest measles epidemic in the United States in nearly 50 years, with pediatric deaths numbering in the hundreds within five years. Those deaths are a model output over five years, not the CDC’s 2026 death tally of 2, which the agency says may change as records are reviewed. CDC counted 3 measles deaths in 2025.

Nearly 50 years back from 2026 lands in the late 1970s, when reported measles still ran in the tens of thousands. In 1977 the United States counted 57,345 cases. The 1989-1991 resurgence, driven largely by unvaccinated preschoolers in cities, produced 55,685 cases and 123 deaths, according to a Journal of Infectious Diseases review of elimination strategy.

U.S. MEASLES, THEN AND NOW

Before the 1963 vaccine, roughly 500,000 measles cases were reported each year and about 500 people died. The Maryland team says simulated drops in MMR coverage after a school-rule repeal push outbreak sizes back toward those prevaccine orders of magnitude, with children taking the worst of it.

What Happens if Florida Drops the MMR Mandate?

If Florida repeals school-entry MMR, the model says coverage falls further among children, assortative mixing among kids amplifies each missed dose, and large outbreaks become much more likely, with a chance that measles settles into endemic circulation inside the state and seeds other states. Adult catch-up and short-term steps such as masks and isolation trim severity. They do not close the gap the authors measure when childhood MMR falls.

Gumel has joint posts at Maryland’s Institute for Health Computing and the Institute for Physical Science and Technology. He has watched school-entry rules hold herd immunity in place for decades, and he does not treat the substitutes as equal.

WHAT THE AUTHORS SAY CANNOT REPLACE CHILDHOOD MMR

• Adult catch-up shots: They can blunt an outbreak in older people but cannot make up for missed doses in children, who mix harder.
• Masks and isolation: Useful when cases appear, and Florida has often resisted those steps, they slow spread only while people use them.
• A rights-only frame: Oveson said dropping the school rule would suggest vaccination is unnecessary, which she called inaccurate and dangerous.

The work was funded by the U.S. National Science Foundation under award DMS-2052363, later transferred to DMS-2330801. The paper’s title is “Projected effects of removing school-entry vaccination requirements on measles transmission in Florida.”

The School Rule Florida Has Not Repealed

The politics and the math are on different clocks. Surgeon General Joseph Ladapo, standing with Gov. Ron DeSantis, said on September 3, 2025, that Florida would work to end every vaccine mandate in state law. MMR, mumps, and polio requirements live in statute. The Legislature has to move them. It did not, in the session that followed.

What the health department could touch by rule is a shorter list. In August 2026 it filed a proposal to drop school shots for hepatitis B, chickenpox, Hib, and pneumococcal disease. That rule has not taken effect, and a physicians’ group has asked for a hearing. Children still need those four shots, and they still need MMR, to enroll.

FLORIDA’S MANDATE ROLLBACK, ON PAPER

1. September 3, 2025: Ladapo, with DeSantis, announces a plan to end all school vaccine mandates.
2. September 2025: On CNN, Ladapo says his department ran no outbreak projections and calls the dispute one of parents’ rights.
3. August 2026: The Florida Department of Health files a proposed rule to drop four non-MMR school shots. The measles requirement stays in statute.
4. September 28, 2026: Oveson and Gumel publish the Florida measles model in PNAS.

So the paper is not scoring a law that already passed. It is scoring a policy Florida’s top doctor still wants, against coverage that has already sagged with the old rule in force. That is the second shock in the results. The mandate is leaky now. Kindergarten MMR at 88.9% is the proof.

Ladapo Said He Did Not Need a Model

A year before the Maryland paper, Florida’s surgeon general was asked whether the state had projected measles, polio, or whooping cough if school rules fell. He said the department had not, and that he did not think modeling was required.

Ultimately, this is an issue very clearly of parents’ rights. So do I need to analyze whether it is appropriate for parents to be able to decide what goes into their child’s body? I don’t need to do an analysis on that.

Joseph Ladapo, Florida surgeon general, on CNN

He has also said Florida already manages outbreaks the way every state does, with no special new playbook. The Maryland paper answers a different question: what happens to epidemic size when the childhood share of immunity falls, in a virus that infects close to nine in ten unprotected people who are exposed. Gumel’s reply to the substitute-tools argument is that adult shots and short-term behavior change cannot compensate for declines in childhood MMR coverage.

Oveson pointed to national survey data showing that 16% of parents are not confident the MMR vaccine is safe for children, 17% believe the risks outweigh the benefits, and 18% fully oppose school-entry MMR mandates. Gumel said health officials have to reach those parents if they want to prevent or contain the outbreaks he expects, because the virus is circulating, coverage is down, and children are back in school.

Measles Would Not Stay Inside State Lines

Gumel called Florida an “extremely important case study with ramifications well beyond the southeastern United States.” The paper’s last turn is geographic. If measles becomes endemic in Florida, the state is not only a local disaster. It is a reservoir. People move. So does a virus with a two-week infectious window and a long record of riding airports and family visits.

The 2026 map is already national. CDC logged cases in 47 jurisdictions plus 17 among international visitors, and 40 new outbreaks. Of the 3,659 cases, 3,478, or 95%, were outbreak-associated. Pennsylvania had 850 cases through September 24, South Carolina 670, Utah 535, and Texas 192. Florida’s 148 cases already dwarf the 8 the state recorded in all of 2025, and the 11 it recorded in 2024.

THE 2026 U.S. FILE, IN FOUR LINES

• The count: 3,659 confirmed cases through September 24, already above 2025’s 2,289 and 2024’s 285.
• The kids: 43% of cases are ages 5 to 19, the group that sits in the rooms a school mandate is built to cover.
• The shots: 95% of patients were unvaccinated or of unknown status.
• The hospitals: 9% of cases were hospitalized, including 14% of children under 5.

Florida can leave MMR in statute and still sit under 95%. It can also take the last rule off the books and, in this model, hand a childhood-driven wave a wider door. Neighboring states that kept school MMR would still take the travel cases. The authors’ warning is that a coverage miss this large does not respect a state line, and that the group that would spread it fastest is the group the school rule was written to cover.

Disclaimer: This article is news reporting on a peer-reviewed mathematical model and on public case and coverage figures. It is informational only and is not medical advice, a diagnosis, or a recommendation about any person’s vaccination, school enrollment, or treatment. Readers who have questions about measles, MMR doses, or school immunization rules should consult a licensed physician, pediatrician, or their local health department before making a health decision. Case counts, death tallies, coverage rates, and the status of Florida’s proposed rule changes reflect the sources as dated above and may be revised as agencies update their files.