AUSTIN, Texas — Georgia Moore was diagnosed with leukemia the day after her 10th birthday. The fourth-grader began an intense chemotherapy regimen, which left her immune system vulnerable and kept her from attending her private Montessori school.

But her younger sister Ivy was in kindergarten at the same school, where a few families opted out of vaccinating their children. That meant 6-year-old Ivy might bring home germs that could threaten Georgia.

“She would go to school, come home and immediately we’d put clothes in the washer to keep a healthy environment,” the girls’ mother, Courtney Moore, said of the family’s after-school routine.

Georgia, now 16, had very few hospitalizations during the course of her treatment and is now cancer-free and five years out of treatment. But Georgia’s fight against cancer made Courtney Moore a vocal advocate for immunizations in Texas — where an increasing number of parents are choosing not to vaccinate children.

Texas is one of 18 states that allow nonmedical exemptions to the vaccines required for school attendance. California had a similar law until last year when it enacted a law that has one of the strictest requirements in the country after a 2014 outbreak of measles infected more than 600 people around the country.

Many of the parents opting out of immunization, which is widely recommended by doctors, say they fear a link between the vaccines and health problems such as autism. But studies that they cite have been widely debunked by public health officials.

“Year after year we’ve seen a steady increase in the number of students with a conscientious exemption from vaccination in Texas,” said Christine Mann, a spokeswoman for the Texas Department of State Health Services. “But overall, the numbers are small.”

Even though statewide levels of vaccinations remain high, at over 98 percent, what concerns public health officials are the growing clusters of geographic areas with high rates of unvaccinated children. Texas went from just 2,314 “conscientious exemptions” in 2003 to 44,716 this year, according to the Texas Department of State Health Services.

Some parents are pressing state officials to let them know how many of their children’s peers are unvaccinated. Jinny Suh, who has a 4-year-old son, is helping spearhead a petition drive asking legislators to change state law so that the number of school exemptions is public. Currently, exemption rates are available for individual private and charter schools, but only districtwide for public schools.

State Rep. Cesar Blanco, a Democrat from El Paso, introduced a bill that would require schools to notify parents about vaccination rates at the school level, but the bill was stalled in committee.

“As a parent, there are lots of things that people get very passionate about,” Suh said, “but for some reason, in my experience, vaccinations remains an almost taboo topic besides a few passionate people.”

As is the case across the country, areas where chidren aren’t being vaccinated in Texas tend to be places with more highly educated and higher-income residents. The school with the highest percentage exemption rate in the state is the Austin Waldorf School, where more than 40 percent of students are unvaccinated. Regents Academy, a private school in East Texas, has the second-highest exemption rate, at almost 38 percent.

“If one of those kids is incubating an infectious disease and the other kids aren’t vaccinated, then it’s going to spread like wildfire,” said Catherine Troisi, an infectious disease epidemiologist at the University of Texas Health Science Center at Houston.

Troisi said that for a disease like measles, you want “herd immunity” to be at 95 percent to prevent an outbreak. If healthy children aren’t receiving vaccines, they are putting children who are too young to receive the vaccine and people with compromised immune systems at a much greater risk of infection.

The American Academy of Pediatrics in September issued a statement encouraging pediatricians to be more vocal about the importance of vaccines for children healthy enough to receive them.

But some parents are leery.

“We believe parents should make medical decisions for their children, not the state,” said Jackie Schlegel, director of Texans for Vaccine Choice, a political action committee that was formed partly in opposition to 2015 legislation to do away with the state’s nonmedical vaccine exemptions.

“We campaigned, we block-walked and we’ll do it again for anyone else who would like to trample on our parental rights,” Schlegel said. When asked if she supported a parent’s right to know the number of unvaccinated children at a given public school, Schlegel said “informed consent and privacy are very big concerns and need to be evaluated on both sides of the coin.”

Others are even more adamant in their opposition. “That’s a slippery slope,” said Del Bigtree, one of the producers of “Vaxxed: From Cover-Up to Catastrophe” a 2016 film that claims a link between autism and vaccines and alleging the federal scientists have covered up the research. It was directed by Andrew Wakefield — the former British gastroenterologist now living in Texas who wrote a discredited research paper linking vaccines to autism in 1998.

As a mother who has seen the issue up close, Moore hopes parents understand how their decision not to vaccinate their child could have far-reaching consequences.

“It’s a very personal decision…” Moore said. “But you have to recognize that if you choose not to [vaccinate], there’s a good possibility that that personal decision will impact a lot of people.”

Kaiser Health News (KHN) is a national health policy news service. It is an editorially independent program of the Henry J. Kaiser Family Foundation.