A modeling study estimates that a further 5% drop in kindergarten measles, mumps, and rubella (MMR) vaccination would substantially increase outbreak magnitudes in Texas counties, and another analysis suggests that restricting non–medical exemptions (NMEs) for the vaccine would increase uptake in the United States.
The findings came as the Advisory Committee on Immunization Practices (ACIP), which makes vaccine recommendations to the Centers for Disease Control and Prevention (CDC), voted to stop recommending the MMRV (measles, mumps, rubella, and varicella [chickenpox]) vaccine for children younger than 4 years old in favor of separate MMR and chickenpox shots. It also voted to end coverage of the vaccine through the Vaccines for Children program.
Increase in vaccination may keep cases down
Led by University of Texas researchers in Houston, the first study was published late last week in JAMA Health Forum.
Even if some assumptions are later disproven, simulating a range of carefully constructed scenarios can meaningfully contribute to pandemic preparedness.
The team used a mathematical model first calibrated using local measles vaccination rates and case data from Gaines County in West Texas, where the first four measles cases of the state outbreak were identified in January 2025.
The authors used the model to estimate potential outbreak sizes in different Texas counties through June 2025 under three scenarios: 1) reported vaccination rates for each county (baseline); 2) a 5% reduction in vaccine uptake; and 3) a 5% increase in vaccine coverage.
After the MMR vaccine was introduced in the United States in 1971, infections fell steeply, and the disease was declared eliminated in 2000. But in recent years, vaccination in the United States has declined, fueled by misinformation campaigns. By the end of the West Texas measles outbreak in August, 762 people had been infected, 99 had been hospitalized, and 2 children had died.
“These events underscore the challenges in maintaining community immunity in the setting of vaccine hesitancy and disruption of routine vaccination programs, including drops in MMR coverage,” the researchers wrote.
The kindergarten MMR vaccination rate in Texas fell from 98.5% in 2013-14 to 94.3% in 2024-25. In Gaines County, it dropped even more, from 92.6% to 82.0% over the same periods.
Under the baseline scenario across all Texas counties, Gaines and Walker counties were estimated to have 14 measles cases per 1,000 people, with 13 per 1,000 in Brazos, Erath, and Kent counties and 12 per 1,000 in Sterling County.
Under the 5%-reduction scenario, outbreaks expanded substantially, with 21 cases and 4 hospitalizations per 1,000 in Gaines; 16 and 3 per 1,000in Walker; 14 and 3 per 1,000 in Brazos; and 15 and 3 per 1,000 in Erath. But if all counties increased their vaccination rates by 5%, no county was projected to exceed 15 cases and 3 hospitalizations per 1,000.
“Even if some assumptions are later disproven, simulating a range of carefully constructed scenarios can meaningfully contribute to pandemic preparedness,” the authors concluded.
‘Urgent need for evidence-based policy reform’
For the second study, published last week in Vaccine, a team led by Johns Hopkins University researchers analyzed the relationship between NME policies and MMR vaccination trends in 33 states before the COVID-19 pandemic and during the 2022-23 and 2023-24 school years.
These outcomes are of particular importance given recently passed and pending state legislation to increase access to vaccination exemptions in over 15 states.
In total, 26 of 33 states experienced statistically significant changes in county-level MMR vaccination rates from 2017-18 through 2023-24, and only 4 (California, Connecticut, Maine, and New York) saw a statistically significant increase. Of the four states, New York, Maine, and Connecticut repealed NME options in 2019, 2021, and 2021, respectively, while California’s NME prohibition policy remained in place for the entire study period.
In contrast, states with the largest (and statistically significant) declines in MMR rates are those that allowed both religious and philosophical exemptions (ie, had the most avenues for parents to opt out of vaccines for their children). Of the six states with insignificant changes in MMR rates, two (Rhode Island and Hawaii) were due to small sample sizes, while Colorado, Nevada, Maryland, and Vermont reflected only slight changes in MMR uptake.
The researchers then expanded the analysis to include 49 states, each assigned to one of four groups based on their NME policy or policy change. The groups were those that 1) prohibited all NMEs (NME_0), 2) allowed religious exemptions (NME_1) or religious and philosophical exemptions (NME_2), and 4) changed their policy to remove all NMEs during the study period (NME_3).
The three NME_0 states that prohibited NMEs (NME-0) reported a slight average decline in MMR vaccination rates (0.8%), from 98.1% to 97.3%, with rates above the desired 95% herd-immunity threshold. For the 28 NME_1 states, MMR rates fell by an average of 2.3%, from 94.4% to 92.1%.
Among the 15 NME_2 states, rates declined 3.8%, from 93.3% to 89.5%. For NME_1 and NME_2, average MMR rates fell below 95% across the study period. In contrast, the three NME_3 states recorded a 1.7% increase, from 96.0% to 97.6%. The authors noted that the NME_0 and NME_3 groups were too small to conduct a meaningful statistical comparison.
“These outcomes are of particular importance given recently passed and pending state legislation to increase access to vaccination exemptions in over 15 states, exemplified by Texas, West Virginia, and the unprecedented announcement of plans to repeal all vaccine mandates in Florida,” they wrote.
“These state-led efforts in combination with changes to the CDC’s vaccination recommendations and the relevant advisory process highlight the urgent need for evidence-based policy reform to protect public health in the U.S.,” they concluded.