In communities nestled among the red sandstone cliffs and riparian forests of southern Utah, measles took hold last summer. At the main school in Hildale, a town along the Arizona border, just 30% of kindergartners are considered adequately immunized by Utah’s health department, meaning they’ve gotten recommended vaccines against measles, tetanus, polio, and more. Exemptions from childhood vaccine requirements are easily acquired in the state: Parents need only claim personal, religious, or medical reasons.

Many people in Hildale and the surrounding towns are connected to the Fundamentalist Church of Jesus Christ of Latter-Day Saints, a sect that has been leery of the government since a police raid in 1953 separated polygamous parents from their children. Shirlee Draper, a southern Utah resident who grew up in the faith, said they became ever more isolated in the early 2000s under the leadership of Warren Jeffs. Before he was sentenced to life in prison for sexual assault against minors, Jeffs instructed his followers to withdraw from public schools and mainstream medicine.

“Growing up, we all got our vaccines,” said Draper, who left the group during Jeffs’ reign. “It wasn’t until Warren Jeffs came along that there started to be more and more resistance.”

After Jeffs went to prison, many people left the faith but remained concerned about vaccines because of online misinformation, such as claims that the shots are toxic. Today a small shop in Hildale sells mouth sprays and oral drops professing to detoxify vaccines. Water, glycerin, and “whole grain alcohol” are listed as ingredients in one called Vxx-Dtx.

As usual, a big driver behind anti-vaxx sentiment is religion and lack of education. It only took a couple generations to overturn the strides we made with vaccines in these communities. And now herd immunity is gone.