"We’re in for some rough sledding next legislative session," said a prominent vaccine advocate.

At around midnight on primary night in Dallas, Lisa Luby Ryan was flanked by two leaders of Texans for Vaccine Choice, arms raised, cheering.

“We just got a call from Representative [Jason] Villalba, who conceded to us and wished us well,” said Ryan, the far-right challenger to the GOP incumbent. Jackie Schlegel, executive director of Texans for Vaccine Choice, and Rebecca Hardy, its state policy director, wore Ryan campaign shirts and huge grins. “Victory!” they shouted.

Schlegel’s feud with Villalba began in 2015, when the Dallas Republican led legislation, ultimately unsuccessful, to eliminate nonmedical “conscience exemptions” for vaccination in public schools. A mother who says one of her kids was injured by vaccines, Schlegel created the now-influential group, which she argues is not anti-vaccine but pro-parental rights. In the months before the primary, members of the group block-walked, raised funds and posted on social media in support of Ryan and other candidates.

“I am so proud of the work we have done here,” Schlegel said to Ryan, who noted that she couldn’t have won “without my amazing group of moms who believe in the power of family.”

In February, the moderate-ish Villalba told the Observer the anti-vaxxers were “so insignificant to my campaign … they’re as important to me as the Flat Earth Society.” But he ended up losing his seat by about 6 percentage points — Texans for Vaccine Choice’s biggest win.

Whether the group was responsible for defeating Villalba may be less relevant than whether lawmakers believe it was. Representative Sarah Davis, another target of anti-vaxxers, said Texans for Vaccine Choice has “bullied and intimidated” many of her colleagues. She said she couldn’t get hearings on her pro-vaccine bills last session.

Davis defeated her own far-right primary challenger, Susanna Dokupil, and anti-vaccine activists’ bid to take down Representative J.D. Sheffield, a Republican doctor, also failed. But Schlegel called Ryan’s win “just the beginning.”

Villalba declined to file his vaccine bill again in 2017 after Texans for Vaccine Choice campaigned against him in 2016, saying he wasn’t interested in a “suicide mission.” Asked what his loss may mean for future vaccine legislation, Villalba wrote in a text, “I suspect [Davis] remains dedicated to ensuring that all Texans continue to receive the benefit of modern medical science, including proper and necessary vaccinations.”

Meanwhile, the number of vaccine exemptions for reasons of conscience in Texas schools has skyrocketed from about 2,300 — when they were first allowed in 2003 — to nearly 53,000 last year. “I’m worried about the increasing erosion of the number of kids who are vaccinated, and I continue to be worried about a new disease outbreak,” said Peter Hotez, director of the Texas Children’s Hospital Center for Vaccine Development. Six people, all unvaccinated, were infected in a measles outbreak in Ellis County in January, and Hotez warns that a larger outbreak could be around the corner.

Whether the group was responsible for defeating Villalba may be less relevant than whether lawmakers believe it was.

Villalba’s loss is “concerning because he was an important pro-vaccine champion,” Hotez told the Observer the day after the primary. “I’m concerned that he’s now out by a candidate backed by the anti- vaccine lobby. … We’re in for some rough sledding next legislative session.”