Texas Cities More Susceptible to Measles Outbreaks
could spread from person to person. In 2015, California legislators used FRED to help convince their peers to pass a bill restricting vaccine exemptions for school-age children.
The Texas Pediatric Society asked Pitt Public Health to model Texas in FRED to demonstrate the possibility of outbreaks in communities with low vaccination rates. Texas is the largest state by population that allows parents to opt their children out of required vaccines for religious or personal reasons. These exemptions have increased 28-fold in Texas, from 2,300 in 2013 to 64,000 in 2016. Austin is the current home of Andrew Wakefield, a discredited former British doctor who published falsified research linking vaccines to autism and who continues to espouse anti-vaccine messages.
In the FRED Measles Texas simulation, a single case of measles is introduced into various metropolitan areas through a randomly selected student whose parents have refused to vaccinate. The simulation runs for each city for 270 days — the length of the typical school year — at current vaccination rates and at a hypothetical decrease in those rates.
At current rates, the simulation estimates that measles outbreaks of more than 400 cases could occur in Austin and Dallas-Fort Worth. This is partly due to a minority of schools where vaccination rates are less than 92 percent — low enough for measles to sustain transmission.
If the vaccination rate drops 5 percent in only the schools with populations that currently are undervaccinated, the size of potential measles outbreaks climbs exponentially in every metropolitan area, with Dallas-Fort Worth, Austin and Houston all susceptible to outbreaks of 500 to 1,000 people.
Approximately 64 percent of the simulated cases occur in children who were unvaccinated because they had a religious or personal exemption. But the model forecasts 36 percent of the cases would be in people who have a medical condition that prohibited vaccination, whose vaccine failed to build immunity or in unvaccinated adults, for whom the risk of complications is higher than children.
“When someone refuses to be vaccinated, they are making a decision that doesn’t only impact them. They are increasing the risk that people who are not immune, through no fault of their own, will get very sick and possibly die,” said senior author Mark Roberts, M.D., M.P.P., professor and chair of Pitt Public Health’s Department of Health Policy and Management, and director of Pitt’s Public Health Dynamics Laboratory.
