Stanford University Simulation Model Paints Grim Picture If Measles, Mumps, and Rubella Vaccination Rates Continue to Drop
Even a 10% decline in vaccination rates would cause cases to skyrocket, leading to massive increase in demand for clinical laboratory MMR testing
As policymakers consider revisions to the current childhood vaccination schedule, a simulation model developed at Stanford University projects that declines in vaccination rates could lead to a dramatic resurgence of measles and other preventable infectious diseases over the next 25 years. Even at current vaccination rates, measles could once again become endemic in the US within two decades, the researchers reported.
The model suggests that clinical laboratories could one day find themselves testing millions of children for diseases once thought to be nearly eliminated in the US.
“With measles, we’re right on the cusp,” said senior author Nathan Lo, MD, PhD, assistant professor of infectious diseases, in a Stanford Medicine press release. “Increasing vaccination levels by just 5% brings the number of measles cases down, safely away from returning to endemic levels.”
The study, titled, “Modeling Reemergence of Vaccine-Eliminated Infectious Diseases Under Declining Vaccination in the US,” appeared April 24, 2025, in the Journal of the American Medical Association. In addition to the Stanford researchers, Peter J. Hotez, MD, PhD, of Baylor University and the Texas Children’s Hospital Center for Vaccine Development, contributed to the study.
“We’ve seen a worrisome pattern of decreasing routine childhood vaccinations,” said study senior author Nathan Lo, MD, PhD, in a Stanford Medicine press release. (Photo copyright: Stanford University.)
Millions of Measles Cases Predicted if Vaccinations Drop
To complete their study, the researchers looked at four infectious diseases:
- measles,
- rubella,
- poliomyelitis, and,
- diphtheria.
“We used a large-scale epidemiological model to simulate all individuals living in the US and assigned them an age, vaccination status, immunity, state of residence, etc.,” Lo explained. “We then simulated how infections would spread under different vaccine conditions.”
Each state was modeled independently to account for variations in risk, noted lead author Mathew Kiang, ScD, assistant professor in the department of epidemiology and population health at Stanford. For example, Massachusetts is considered low risk due to high vaccination rates, whereas Texas and California are “higher risk because vaccination rates in both have dropped and there’s a lot of travel to those states,” he said.
The model assumed that infections would not cross state lines, “so the numbers could be an underestimate,” Kiang said.
He painted a grim picture of the scenarios projected by the model.
“If vaccination were to fall by even 10% today, measles cases would skyrocket to 11.1 million over the next 25 years,” he said. “If vaccination rates were cut in half, we’d expect 51.2 million cases of measles, 9.9 million cases of rubella, 4.3 million cases of polio, and 200 cases of diphtheria over 25 years. This would lead to 10.3 million hospitalizations and 159,200 deaths, plus an estimated 51,200 children with post-measles neurological complications, 10,700 cases of birth defects due to rubella, and 5,400 people paralyzed from polio.”
Lo suggested a more hopeful scenario in which “some fraction of the unvaccinated population seeks vaccination” as the diseases spread over the next decade. However, “if that were to happen, you can’t just flip a switch—once these diseases get unleashed, it would take time eliminate them again,” he said.
As of May 22, 2025, 1,046 cases of measles have been reported in the US this year, according to the Centers for Disease Control and Prevention. This year has been among the most active for measles since 2000. For the whole of 2024, 285 cases were reported.
More Contagious than COVID-19
All four diseases are far more contagious than COVID-19, Lo said, but measles “is in a different ballpark” as one of the most infectious diseases known to medicine. In a fully susceptible population, he said, one person can infect up to 20 individuals, but for the purposes of the simulation, they used a more conservative estimate of 12.
“There was a disruption to healthcare services during the pandemic, but declines preceded this period and have accelerated since then for many reasons,” he noted. “People look around and say, ‘We don’t see these diseases. Why should we vaccinate against them?’ There’s a general fatigue with vaccines. And there’s distrust and misinformation about vaccine effectiveness and safety.”
Another concern with measles is that the MMR vaccine “has become particularly controversial, partly due to a history of fraudulent medical research that raised safety concerns,” Lo said.
He added that compared to the other diseases, measles is more prevalent globally.
“Travelers importing a disease are like matches, and US under-vaccination is the tinder,” Kiang said. “With measles, you’re throwing a lot of matches in, and eventually something is going to happen.”
—Stephen Beale
