Julie Thannum, assistant superintendent for board and community relations for Carroll ISD, said the district does not find its exemption rate alarming as neighboring districts, such as Northwest ISD—which has a rate of 2.7 percent—and GCISD have higher exemption rates.

“If our exemption rate was significantly higher than our neighboring districts, then I think we would find it alarming,” she said. “We would work to find out why our exemption rate is growing faster than theirs and what they are doing differently than us.”

The trend, if it continues on its current trajectory, threatens to undermine what vaccine researchers call herd immunity. Herd immunity is when a population’s high vaccination rate helps slow the spread of vaccine-preventable diseases, protecting the unvaccinated and people for whom vaccines are not fully effective.

“You need a certain amount of people to be vaccinated to protect the community at large,” said Dr. Lynne Eger, who treats infectious diseases at Cook Children’s Medical Center in Fort Worth. “There is probably no vaccine that is 100 percent protection, so you need herd immunity. The higher the number of people who are not vaccinated, the more risk those people are putting the entire community at.”

Although the state health agency does not yet recognize a significant concern statewide as a result of the trend, an agency spokesperson said the risk of outbreaks increases as vaccination rates continue to decline in school districts throughout Texas.

“There’s not a number that I think we can point to that at ‘X,’ it’s going to be a problem,” said Chris Van Deusen, a spokesperson for the agency. “It’s really kind of a sliding scale, if you will. The more unvaccinated individuals you have, the more likely you could have some sort of outbreak.”

In neighboring Denton County, where nearly 3 percent of students countywide have received conscientious exemptions, a top health official says herd immunity is already being undermined.

“Having twice the state average, that’s a concern to us, because we believe vaccines are a good way to prevent communicable and infectious diseases,” said Matt Richardson, Denton County director of public health.

Policy and demographics

There were two proposals that failed that were under consideration in the Texas Legislature this session that would have made it more difficult for parents to obtain an exemption. House Bill 241 would have required a doctor’s consultation before parents obtain an exemption; HB 126 would have required parents to first review online educational materials.

Some groups organized to lobby against legislative efforts to curb exemption rates, including Texans for Vaccine Choice, based in Keller.

“These bills would place a barrier between parents and their exemptions,” the group’s Director of State Policy Rebecca Hardy said. “These bills also assume the parents that are requesting these exemptions are uneducated, when in fact all the research shows that those that choose personalized vaccination schedules are, in fact, quite educated.”

A government study of data from the 2009 National Immunization Survey found parents who delay or refuse vaccinations for their children are more likely than the average person to have graduated from college and have an annual household income of at least four times the federal poverty line, among other factors associated with higher socio-economic status.

In Southlake, the median 2015 annual household income was $183,123, and more than 40 percent of adults age 25 and older had at least a bachelor’s degree, compared to 30 percent nationwide, according to U.S. Census surveys. In Colleyville, the median 2015 annual household income was $152,310, and more than 40 percent of adults age 25 and older had at least a bachelor’s degree. Grapevine’s 2015 median annual household income was $79,083, and 31 percent of adults 25 and older had at least a bachelor’s degree.

The Centers for Disease Control and Prevention analyzed survey responses from a sample of 11,206 children and determined children were vaccinated at lower rates across the board if their parents believed vaccinations could result in serious side effects or that too many vaccines could overwhelm a child’s immune system.

The study also found parents who delayed and refused vaccines are more likely to be white.

Hardy, after citing examples of private and charter schools that have high exemption rates and no recent disease outbreaks, said her group promotes access to exemptions without weighing in on the scientific consensus on declining vaccination rates and herd immunity.

“They’re following their religious and other deeply held convictions,” Hardy said of parents seeking exemptions.

But state health officials say such examples of small populations that avoid outbreaks are not reflective of the broader risks associated with declining vaccination rates.

For an outbreak to occur, Van Deusen said, it is not enough to simply have low vaccination rates; the disease, made rare by the widespread use of vaccines, must also be reintroduced to the population.

Local protocol

CISD and GCISD officials have protocols for preventing and responding to outbreaks of disease.

Both districts provide information to parents, students and staff on how to prevent the spread of an illness.

“In GCISD we take several measures to provide a reasonably safe environment; however, we cannot guarantee [we are] risk-free,” Director of Health Services Amy Howard said. “We have a great relationship with Tarrant County Public Health and communicate with officials regularly to determine if there are any necessary updates or information that needs to be shared with our families.”

In the event of an outbreak, the districts would report the illness to health authorities.

“Our district works very closely with Tarrant County Public Health, attending monthly meetings with other districts in our region, getting the latest updates on outbreaks and management,” said Karen Flexer, CISD’s lead nurse. “We follow TCHD epidemiology orders specifically to ensure CDC compliance to protect and teach our families about communicable diseases.”

The state health agency compiles the exemption rates each year but does not analyze it in great detail, leaving that up to independent researchers, Van Deusen said. And since there is no hard-and-fast cutoff for what exemption rates are considered too high, the state offers districts little guidance.

“We can’t twist people’s arms, and we can’t force vaccinations, because exemptions are legal—that’s a right that people have,” Van Deusen said. “We fall back on the science and we talk about the benefits of immunization and how important they’ve been over the decades, since they were one of the ultimate achievements of public health in the 20th century.”