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Florida's plans to cut vaccine mandates in schools could trigger the country's largest measles outbreak in 50 years, a new study has found.
Researchers at the University of Maryland used a mathematical model to determine the impact of Florida dropping the measles, mumps and rubella (MMR) vaccine from child immunization mandates.
The results indicated that the move could trigger the largest measles epidemic in the U.S. in nearly half a century, with projected pediatric deaths numbering in the hundreds within five years.
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The study was published in the journal Proceedings of the National Academy of Sciences on September 28.
Last year, Florida Governor Ron DeSantis vowed to end all vaccine mandates in the state—which would make it the first state to do so—and last month, a proposal, signed by Florida Surgeon General Joseph Ladapo, suggested that students entering pre K-12 classes would no longer have to be vaccinated against Hepatitis B, varicella (chicken pox), Haemophilus influenzae type b (Hib), and pneumococcal conjugate. The MMR vaccine was not included, and is still currently required by state law.
The state's rate of vaccine exemptions for kindergartners is already higher than the national average, and MMR vaccine coverage is lower than the country's average as well, according to data provided by the Centers for Disease Control and Prevention (CDC). Despite measles being considered eradicated in 2000, this year America has experienced its highest caseload of measles in over three decades (with over 2,000 cases recorded so far this year). Over 100 of those cases have been recorded in Florida.
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What The Study Found
Researchers at the University of Maryland built a model based on a 2025 measles outbreak in Gaines County, Texas, and incorporated Florida-specific demographic structure, MMR vaccination coverage data, and realistic mixing patterns across ages and geographies.
The model showed that simulated declines in MMR vaccination coverage following removal of school-entry requirements, alongside Florida’s already low vaccine-induced herd immunity threshold, increased large-outbreak potential with pediatric deaths in numbers not seen since pre-vaccine eras.
The findings indicated that even small reductions in child vaccination rates could lead to "disproportionately large increases in the scale of outbreaks," the paper’s first author, Alice Oveson, a Ph.D. student in applied mathematics and statistics, and scientific computation at the University of Maryland said.
The team also said that ending the MMR vaccine mandate would not only make measles endemic in Florida, but it could also reignite transmission across the U.S.
"The results of the study confirm what we already know," Dr. Jon Andrus, a professor of global health at George Washington University, told Newsweek. "Removing school entry MMR vaccination requirements would be disastrous to the health and well-being of the children of Florida, and potentially spearhead an even larger outbreak across the country."
The Impact Of Child Immunization Against Measles
Dr. Paul Offit, director of the Vaccine Education Center and an attending physician in the Division of Infectious Diseases at Children's Hospital of Philadelphia, told Newsweek that school vaccine mandates are "important" because the measles virus—the "most contagious human infection"—is often transmitted more easily in schools. This means that by reducing the spread of measles in schools, it could reduce the spread in a community as a whole.
He said it is also vital to get the vaccine as a child, because adults are 10 times more likely to be hospitalized when infected and die of measles-associated pneumonia.
He added that if, "in the name of medical freedom," Florida decides to remove vaccine mandates, then that also gives people the freedom to "catch and transmit a potentially fatal infection."
"You're not just making a decision for yourself or for your child, you're making a decision for the community," Offit said.
Andrus said that the combination MMR vaccine is "one of the best childhood vaccines we have. It makes absolutely no scientific, or humanitarian sense to rescind vaccination requirements, knowing the potential for such action to cause harm."
"Even one cohort of undervaccinated children will lead to immeasurable damage," he added. He said that the "potential severity of the disease" make the prospect of ending the MMR vaccine mandate "incredibly concerning."
How Long Could It Take For Measles To Be Endemic in Florida?
Offit said he didn't think it would take "long at all" for measles to become endemic in Florida if the vaccine mandate was lifted, adding that measles cases are already high in the state now.
He said that the number of cases nationwide are also likely to be higher than the recorded number because of the fact that the country has seen several cases with "rare complications." Given their rarity, he said it suggests there is likely an "underestimation of the number of cases."
Meanwhile, he also said that it could take "years if not longer to rebuild" the 95 percent herd immunity threshold in the state. The 95 percent herd immunity threshold refers to the vaccination coverage percentage believed (by the World Health Organization) to be necessary in order to establish herd immunity in an area.
What Needs To Be Done?
Paper co-author Abba Gumel, a professor of mathematics at the University of Maryland, said that "what’s most troubling is that we know these mandates effectively prevent erosion of herd immunity."
"Strengthening adult immunity through catch-up vaccination could help reduce the severity of outbreaks, and as-needed behavioral interventions like masking and isolating could slow transmission," he added. "But neither can compensate for declines in childhood MMR coverage."
Oveson said that suggesting vaccination is "unnecessary" by removing the mandate is "simply inaccurate and dangerous," noting that the study provides quantitative evidence that such a policy change could make measles endemic in Florida and potentially reignite transmission across the U.S.
“Public health officials need to find ways to reach these parents if they are to prevent or contain future measles outbreaks, wherever they occur,” Gumel said. “And they will occur—the disease is out there, vaccination coverage is down, kids are going back to school and the data and science don’t lie.”
Reference
A. Oveson, and A.B. Gumel (2026) Projected effects of removing school-entry vaccination requirements on measles transmission in Florida. Proceedings of the National Academy of Sciences. https://doi.org/10.1073/pnas.2610455123.
Contact Newsweek editors on this story: Kara Dolman and Emma Lee-Sang
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