HOUSTON (AP) – An increasing number of Texas parents are opting to not have their school-age children vaccinated, the state’s health department said.

Although the overwhelming majority of Texas students have received vaccine shots, the state agency reports more than 38,000 were exempted from required vaccinations in the 2013-2014 school year. That’s tripled in the last six years from an estimated 10,400 students in 2007-2008, worrying public health specialists that it will lead to outbreaks of preventable diseases, the Houston Chronicle reported.

“Those are scary numbers,” said Dr. Peter Hotez, dean of the National School of Tropical medicine at Baylor College of Medicine and Texas Children’s Hospital. “Considering how non-vaccinators tend to cluster, they make Texas extremely vulnerable to an outbreak.”

Some parents say they object to vaccines in general because of potential side effects. They are allowed under a law to exempt their child from Texas immunization requirements, including one that protects against measles, which is now spreading in the United States.

Measles is a respiratory disease that spreads through the air through coughing and sneezing. It causes a fever, runny nose, cough, red eyes and a sore throat, followed by a body rash.

More than 100 measles cases in multiple states have been linked to people who visited or worked in December at Disneyland in California, or were exposed to infected people who went there.

___Copyright 2015 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.