Peter Hotez used to worry mostly about vaccines for children in far-away places. An infectious diseases researcher at Baylor College of Medicine in Houston, Texas, Hotez is developing shots against diseases in poorer countries such as hookworm and schistosomiasis.

But now, Hotez is anxious about children much closer to home. The number of schoolchildren not vaccinated against childhood diseases in Texas is growing rapidly, which means that the state may see its first measles outbreaks in the winter or spring of 2018, Hotez predicted in a recent article in PLOS Medicine . Disgraced antivaccine physician Andrew Wakefield has set up shop in the Texan capital, Austin, and a political action committee (PAC) is putting pressure on legislators facing a slew of vaccine-related bills.

"Texas is now the center of the antivaxxer movement,” Hotez says. “There is a big fight coming,” adds Anna Dragsbaek of The Immunization Partnership, a nonprofit organization in Houston that advocates for vaccinations.

Texas still has one of the highest vaccination rates for childhood diseases overall, 97.4%, according to the U.S. Centers for Disease Control and Prevention. But the number of children not vaccinated because of their parents' “personal beliefs”—as opposed to medical reasons—has risen from 2300 in 2003, when such exemptions were introduced, to more than 44,000 so far this year, according to numbers prepared by The Immunization Partnership based on Texas Department of State Health Services data. The actual number may be much higher because an estimated 300,000 Texan children are schooled at home, says Susan Wootton, an infectious disease pediatrician at the University of Texas in Houston; though the law requires these kids to be immunized too, parents don't need to submit proof of vaccination.

Measles is an extremely contagious pathogen and often the first one to spread when vaccination rates dip below about 95%. The risk of outbreaks is even greater because unvaccinated children aren't randomly distributed. In Gaines county in western Texas, for instance, the exemption rate is already 4.8%, and at one school in Austin, it's 40%. "I would describe Texas as sitting on a ticking time bomb," Wootton says.

Not everyone is so gloomy. Some counties in Washington and Colorado have higher levels of exemptions, says immunologist Diane Griffin of the Johns Hopkins Bloomberg School of Public Health in Baltimore, Maryland. “I don’t think that Texas is any worse than a number of other states, but pointing out the problem and the solution is important,” she wrote in an email.

But Hotez believes the situation in the Lone Star State is more perilous. One factor is the arrival of Wakefield, widely seen as the father of the modern antivaccine movement. Wakefield published a paper in The Lancet in 1998 that alleged a link between the MMR vaccine (which combines shots against measles, mumps, and rubella) and autism. Several large studies have failed to find the link, Wakefield's paper was retracted in 2010, and he was disbarred as a physician after the U.K. General Medical Council found him guilty of dishonesty and endangering children. Wakefield has appeared at screenings of his film Vaxxed, released in April, all over Texas and has testified at many city councils, Dragsbaek says. “He is definitely a major influencer.”

Meanwhile, a PAC named Texans for Vaccine Choice has sprung up after state Representative Jason Villalba, a Republican lawyer from Dallas, proposed scrapping nonmedical exemptions last year. (The bill was never voted on.) “While they do not have a whole lot of money, they have a lot of people that they can deploy to interfere in primary campaigns,” Dragsbaek says. “They made Villalba's primary campaign very, very difficult.” Rebecca Hardy, director of state policies at Texans for Vaccine Choice, says the group is not trying to convince parents that vaccines are dangerous, but fighting for their right not to immunize their children. (It's also helping them apply for exemptions.)

Though almost all U.S. states allow religious exemptions from vaccination, only 18 permit exemptions based on personal beliefs; with 27 million residents, Texas is the most populous one. Another hotbed of resistance to vaccines, California, stopped allowing "philosophical exemptions"—which covered religious and personal beliefs—this year, after a measles outbreak that sickened more than a hundred people. The change in legislation led some Californians opposing vaccines to move to Texas, Hotez says.

The Texas legislature is now pondering several bills that would help shore up vaccination. One would make it compulsory for parents to complete an online course before refusing vaccination; another would require them to discuss their decision with a doctor. The bill with the best chances may be one that would allow parents to know the immunization rates at their child’s school. “This does not infringe on anyone’s right to have an exemption, it simply allows parents who need to protect their children to have adequate information to do so,” Dragsbaek says. But Hardy says her PAC is opposed to even this bill: “If it's truly about a parent's right to know the health status of a campus, then why are we not proposing bills that would give the rates of HIV-positive kids on campus, or hepatitis B-positive kids?" she asks.

For Hotez, who has a daughter suffering from autism, it’s a personal issue. Wakefield is preying on parents' fears, he says: "It gets me enraged and it diverts resources away from understanding the real causes of autism, developing better diagnostics, or providing better resources for parents.” He worries that if antivaxxers are successful in Texas, their views may spread across the United States and abroad. Adding to his worries is the fact that President-elect Donald Trump has repeated the discredited claims of a link between autism and vaccines on Twitter and in an interview, and has met with antivaccine activists during his campaign.

Heidi Larson, an anthropologist at the London School of Hygiene & Tropical Medicine who studies public trust in vaccines, says Hotez is right to sound the alarm. "I think it’s important that they bring attention to this trend and not wait for an outbreak,” Larson says.

Correction, 3 December 2016, 2:00 p.m.: A previous version of this story incorrectly said that Villalba's bill had been voted down in the Texas House of Representatives. The bill was refered to committee but not voted on.