Large and small cities in Texas are becoming increasingly vulnerable to measles outbreaks as more parents exempt their children from required vaccinations, according to a new study from the University of Pittsburgh Graduate School of Public Health.
The study found "large measles outbreaks of more than 400 cases could occur in Austin-Round Rock and Dallas-Fort Worth-Arlington" under current vaccination rates. If those vaccination rates were to decrease by another 5% in the state, researchers found, the size of a potential measles outbreak could grow by up to 4,000% in some communities.
“If policy stays as it is and there is no change in the public’s perspective of vaccinations and the importance of vaccinating their children, then the potential measles outbreaks will only get worse,” David Sinclair, the lead author, told KUT.
Texas is the largest state by population that allows parents to opt their children out of vaccinations for nonmedical reasons. Sinclair said that makes Texas an interesting place to study when it comes to measles outbreaks.
“Results in Texas perhaps are more relevant than anywhere else in the country,” he said.
Texas law currently allows parents to not vaccinate their children for reasons of conscience, which could include religious reasons. According to the study, the number of parents claiming these exemptions have skyrocketed in Texas – from 2,300 in 2003 to 64,000 in 2016.
And schools in the Austin area have particularly high rates of these nonmedical exemptions.
Note: Data from the Department of State Health Services' annual survey of immunization status. This map does not include data from students in some classes with fewer than five exemptions or districts with fewer than 65 students.
In Austin ISD, 2.47% of students overall had conscientious exemptions in the 2018-2019 school year, but there are schools with rates well above the statewide rate of 2.15% in that same time period. The International High School, which shares a campus with Eastside Memorial High School, had an exemption rate of 32%. Zilker and Matthews elementary schools had the next highest exemption rates, with 10% and 9% each, respectively.
Exemptions are, by and large, much more common in private and charter schools. The Austin Waldorf School has one of the highest rates of nonmedical exemptions in the state – nearly half (46%) of its 333 students had exemptions last school year. The Austin Discovery School had an exemption rate of 35%, and Valor Public Schools’ South Austin campus had a rate of 26%.
Sinclair said potential outbreaks get worse when there is “geographic clustering” of unvaccinated people.
“If you have just one or two schools where the vaccination rate is 20 or so percent lower than it should be, then that is enough to let measles spread widely in that school,” he said.
Once a large population in one of those schools is infected, Sinclair said, the outbreak can be spread to the larger community outside the school.
According to a press release, the Texas Pediatric Society asked the University of Pittsburgh Graduate School of Public Health to model Texas in a special system Pitt has to create a fake population simulation using U.S. Census data. The modeling system, known as the Framework for Reconstructing Epidemiological Dynamics, then assigns these fake people to move around their communities as folks would move in the real world. The model allows researchers to see how measles could spread from person to person.
Using this simulation model and 2018 school vaccination rates in Texas, researchers concluded there was a “significant chance of outbreaks totaling more than 100 cases” in various parts of the state.
“If the vaccination rate among students in Texas continues to decrease in schools with undervaccinated populations, the potential number of cases associated with measles outbreaks is estimated to increase exponentially,” the researchers wrote.