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Endemic Measles is a Clear and Present Danger, According to Stanford University Modeling Study
At current vaccination rates, measles could become endemic in the US again within 21 years; the threat extends to rubella, polio, and diphtheria, the study found.
A new modeling study from Stanford University predicts that measles could return to endemic levels in the United States within the next 20 years due to declining childhood vaccination rates, with other previously eliminated diseases potentially following suit under more severe vaccination decline scenarios.
"It’s worth emphasizing that there really shouldn’t be any cases at this point, because these diseases are preventable, Kiang stated. "Anything above zero is tragic. When you’re talking about potentially thousands or millions, that’s unfathomable."
The study, published in JAMA, used simulation models to assess the potential consequences of decreasing childhood vaccination coverage for measles, rubella, poliomyelitis, and diphtheria across all 50 states and the District of Columbia over a 25-year period.
Most alarmingly, researchers found that "at current state-level vaccination rates, the simulation model predicts measles may reestablish endemicity (83% of simulations; mean time of 20.9 years) with an estimated 851,300 cases over 25 years." This suggests that the US may be approaching a critical threshold below which measles elimination can no longer be maintained.
If vaccination rates were to decline by 50%, the model predicts catastrophic consequences: 51.2 million cases of measles over a 25-year period, affecting roughly 15% of the entire U.S. population. The US could expect 9.9 million cases of rubella, 4.3 million cases of poliomyelitis, and 197 cases, the team wrote. "Measles would become endemic in less than 5 years, and rubella would become endemic in less than 20. Under these conditions, polio became endemic in about half of simulations in around 20 years," lead author Mathew Kiang, ScD, assistant professor of epidemiology and population health, said in a Stanford statement.
Kiang and colleagues estimate that such a scenario would also lead to unparalleled sequelae, including death and long-term morbidity. "This would lead to 10.3 million hospitalizations and 159,200 deaths, plus an estimated 51,200 children with post-measles neurologic complications, 10,700 cases of birth defects due to rubella and 5,400 people paralyzed from polio," Kiang continued.
Timing Varies by Disease, Geography
The significant variation in how quickly different diseases might return to endemic status reflects the broad range of critical thresholds among the diseases, the authors explained, with measles likely to be the first to pass the "tipping point."
The research team found that under a 50% reduction in childhood vaccination, measles would return to endemicity in 99.8% of simulations at a mean time of 4.9 years, rubella at 18.1 years, poliovirus in 55.6% of simulations at 19.6 years, and diphtheria in less than 1% of simulations.
Kiang et al also identified substantial state-level variation in susceptibility to outbreaks, with Texas at highest risk for measles resurgence. This geographic heterogeneity reflects differences in current vaccination rates across states, which range from 88% to 96% for measles-mumps-rubella vaccination.
“Massachusetts has high vaccination rates and was consistently low risk. Both California and Texas were higher risk, even after accounting for larger population size, because vaccination rates in both have dropped and there’s a lot of travel to those states,” Kiang noted in the statement.
"With measles, we’re right on the cusp. Increasing vaccination levels by just 5% brings the number of measles cases down, safely away from returning to endemic levels. These are the kinds of small percentages that can really be a tipping point," senior author Nathan Lo, MD, PhD, assistant professor of infectious diseases, said. “It’s empowering that a small segment of the population can make a difference here.”
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Under the 5% increase in vaccination scenario, measles cases would drop from 851,300 to just 5,800 over 25 years, according to the simulation, a 99% reduction compared to what would happen with a 10% decline in vaccinations.
Methods, Limitations
The simulation model incorporated state-specific demographic data, population immunity profiles, and infectious disease importation risk. The model accounted for the dynamic nature of disease transmission, where "the overall risk of infection was related to the number of actively infectious persons in the population in a given state," the authors stated
The researchers acknowledge several limitations, including simplified assumptions in disease transmission modeling and the possibility of within-state heterogeneity not captured at the state level. They emphasize that their estimates may be conservative, meaning "the risk of outbreaks and speed of reemergence under declining vaccination may be greater than predicted."
This study provides critical evidence for healthcare providers to communicate with vaccine-hesitant families. The research clearly demonstrates that population-level immunity is reaching a threshold where measles elimination may no longer be sustainable without intervention, the authors cautioned.
"It’s worth emphasizing that there really shouldn’t be any cases at this point, because these diseases are preventable, Kiang stated. "Anything above zero is tragic. When you’re talking about potentially thousands or millions, that’s unfathomable."
