DALLAS (AP) —

Tucked into a hillside not far from a popular nature preserve, the private Austin Waldorf School touts its individualized learning and emphasis on moral purpose. But the school with an enrollment of nearly 400 is different in another way: Nearly half its students forgo vaccinations, one of the highest rates in Texas.

Four years ago fully half its students received a "conscientious exemption" from at least one of the federally recommended vaccinations, a rate that's since dipped slightly to 48 percent, according to figures provided by the Texas Department of State Health Services.

The school is a striking example of a statewide rise in exemptions that concerns public health officials and runs contrary to efforts in California and elsewhere to ensure more students are immunized.

Texas is one of 18 states that allow parents to cite religion or personal beliefs in exempting their school-age children from vaccination. In 2007 there were more than 10,000 students exempted and that number soared to nearly 41,000 in the last school year. Texas began allowing exemptions for reasons of conscience in 2003. A year later, some 3,000 students had received one.

"I'm mostly concerned about parents who request personal exemptions based on reasons of conscience but in fact they're making that choice based on misinformation they've gotten from other sources or perhaps someone outside the medical community," said Dr. Justin Smith, a pediatrician with Cook Children's Health Care System in Fort Worth.

While students who aren't fully vaccinated account for less than 1 percent of the 5.2 million students enrolled in Texas public or charter schools, the rising trend of exemptions has some medical experts worried about outbreaks of disease.

Those fears were highlighted when a child who had traveled abroad went to school early this month in a Dallas suburb and later showed signs of measles. It was the first reported case of the highly contagious virus in Texas in this new year. Measles cases in the U.S. are unusual, although there were 667 reported cases in 2014, mainly due to an outbreak that occurred primarily among unvaccinated Amish communities in Ohio, according to the federal Centers for Disease Control and Prevention.

Smith believes that social media are playing a role in the rise in exemptions.

"There's more a trend in discussing these issues in social media or discussing them interpersonally with other parents and it kind of becomes a group mentality," he said.

Dawn Richardson, a co-founder of the Texas-based Parents Requesting Open Vaccine Education, said more parents are opting to spread out when their children receive a range of vaccinations rather than when a physician or school dictates it must be done. Parents also are concerned with the increase over the last 15 years in the number of vaccines and the dosages that are given, she said. There were 14 vaccinations recommended by the CDC last year, up from seven in 2000.

"Parents are trying to make better decisions and actually tailor the vaccine schedule according to their child," Richardson said.

Critics contend vaccination can result in disabling side effects — most notably in the form of autism, a connection scientific research has debunked — but Smith and other health experts note the overwhelming science points to wide-ranging benefits from immunization.

He said while the vaccination rate in Texas remains high, if the rate were to drop to 90 percent or lower then outbreaks of disease could become alarming.

Kathy McElveen, interim director of the Austin Waldorf School, said any decision on vaccinating students is left to the parents and that the school complies with all state-mandated health standards.

"Just because somebody sought an exemption doesn't mean that a student isn't immunized," she said, explaining that a parent may opt to immunize for measles or chickenpox, but not another disease, such as hepatitis.

The exemption rate in Texas is comparable to other large states. In Florida, which allows for a religious exemption but not one based on personal beliefs, 1.8 percent of kindergarten students last year had an exemption while just over 1 percent of seventh-graders did.

Just over 3 percent of kindergarten students in California were exempted two years ago and that number dropped to 2.54 percent before lawmakers last year adopted a bill that only allows for medical exemptions. That action came after an outbreak of measles at Disneyland sickened more than 100.

California joined Mississippi and West Virginia as the three states allowing only medical exemptions.

Dr. Ryan Van Ramshorst, a pediatrician in San Antonio and member of the Texas Medical Association, said he wishes "we were living in a day and age where laws like that wouldn't be necessary." But he said more must be done to ensure children are fully vaccinated.

"We're going to reach a critical mass in Texas where we're going to have outbreaks if parents don't vaccinate their children," he said.