Falling Vaccination Rates May Bring Back Measles, Polio in US

Declining childhood vaccination rates in the US could lead to the reemergence of once-eliminated infectious diseases like measles, rubella, and polio, according to new research.1 At current coverage levels, measles could become endemic again within 2 decades, and if vaccination drops by 50%, the country could see over 51 million measles cases, 10 million hospitalizations, and more than 159,000 deaths over 25 years.

Model predicts millions of cases, hospitalizations, and deaths if routine childhood vaccination rates decline significantly. | Image credit: Leigh Prather - stock.adobe.com

The study’s findings are especially urgent considering recent political developments that may undermine vaccine policy and public trust. Just days before the release of this modeling analysis, HHS Secretary Robert F. Kennedy Jr dismissed all members of the Advisory Committee on Immunization Practices—a CDC panel historically grounded in scientific expertise—and appointed several individuals with known antivaccine views.2

While Kennedy framed the move as a step toward restoring public confidence, many public health experts warn that the new appointments could signal a dangerous departure from evidence-based vaccine guidance. This shift, coupled with already declining vaccination rates, raises the stakes for potential disease resurgence and underscores the importance of maintaining robust, science-driven immunization policies to prevent the catastrophic outcomes projected in the study.

This stimulation model study is published in JAMA.1

“We found that reductions in routine childhood vaccination will lead to reemergence and return to endemicity for all 4 infectious diseases under certain scenarios of vaccine decline; however, the timing and magnitude of case numbers and their critical population immunity threshold differed substantially by disease,” wrote the researchers of the study. “Under widespread declining vaccination, measles is expected to be the first disease to have large outbreaks and return to endemicity. For rubella, poliovirus, and diphtheria, vaccine coverage levels would have to drop lower for a longer period before outbreaks and sustained transmission are observed.”

To assess the potential impact of declining childhood vaccination rates in the US, researchers developed a simulation model that incorporated data from all 50 states and the District of Columbia. The model used area-specific inputs on demographics, existing immunity levels, and the likelihood of disease importation to estimate the spread of measles, rubella, poliomyelitis, and diphtheria. Scenarios modeled varying vaccination rates over a 25-year period, including baseline projections using data from 2004 to 2023.

The model calculated both the total number of cases and associated complications, such as congenital rubella syndrome, postmeasles neurological effects, and paralytic polio, as well as the probability and timing for each disease to reestablish endemic transmission within the population.

The simulation model revealed that at current state-level vaccination rates, measles is likely to become endemic again in the US, with an 83% probability and a mean time to endemicity of 20.9 years, resulting in an estimated 851,300 cases over 25 years. A 10% decline in measles-mumps-rubella vaccination would lead to approximately 11.1 million measles cases, while a 5% increase in coverage would reduce cases to just 5800.

Under a worst-case scenario of a 50% drop in childhood vaccination rates, the model projected 51.2 million measles cases, 9.9 million rubella cases, 4.3 million poliomyelitis cases, and 197 diphtheria cases, along with 10.3 million hospitalizations and 159,200 deaths. In this scenario, measles would become endemic in just under 5 years, rubella in 18 years, and polio in about half of simulations.

The researchers acknowledged the study had several limitations. The model used simplified assumptions for disease transmission, immunity, social mixing, and demography, which may have underestimated outbreak risk. Within-state heterogeneity in vaccination and transmission patterns was not captured, nor was cross-state spread, likely resulting in conservative estimates. Some parameters, such as importation risk and vaccine effectiveness, were based on imperfect or generalized data. The model also did not account for reactive vaccination efforts, behavior changes during outbreaks, or vaccine status–based mixing.

Despite these limitations, the researchers believe these findings underscore the significant public health risks associated with even modest declines in routine vaccination.

“Based on estimates from this modeling study, declining childhood vaccination rates will increase the frequency and size of outbreaks of previously eliminated vaccine-preventable infections, eventually leading to their return to endemic levels,” wrote the researchers.

References

1. Kiang MV, Bubar KM, Maldonado Y, et al. Modeling reemergence of vaccine-eliminated infectious diseases under declining vaccination in the US. JAMA. 2025;333(24):2176–2187. doi:10.1001/jama.2025.6495

2. Bonavitacola J. Vaccine skeptics among CDC vaccine panel replacements named by RFK Jr. AJMC®. June 12, 2025. Accessed June 24, 2025. https://www.ajmc.com/view/vaccine-skeptics-among-cdc-vaccine-panel-replacements-named-by-rfk-jr