Charter school students in Utah were more than five times more likely than public school students to catch chickenpox at school, according to state data.

The increased risk of chickenpox aligns with vaccination rates, which are far lower in charter schools than in public schools, according to research published this month by the Utah Department of Health. Nonmedical vaccine exemptions are more than twice as common at charter schools in Utah, one of 18 states that allow such exemptions.

Accordingly, rates of chickenpox were higher among charter school students. From 2011 to 2016, the rate of infection among charter school students was nearly double that of public school students, according to the study.

“This report definitely supports the fact that vaccination works,” said Carson Telford, a state epidemiologist who wrote the paper. “We see significantly fewer cases [among those] who are vaccinated. When they do still get an infection, the result is much less severe, with fewer lesions than among those students who are not vaccinated.”

Even more striking was the risk of becoming infected in a school outbreak. About 1,100 students were infected statewide during those five years, the study reports, and 157 of those cases were associated with an outbreak at a school. Although charter schools enroll only about 12% of Utah’s children, charter school students accounted for more than a third of chickenpox infections that occurred in school outbreaks.

The risk of contracting chickenpox in a school outbreak was 5.2 times higher for charter school students than for public school students. Outbreaks at charter schools also infected more students than outbreaks at public schools: 13.3 students per outbreak at charter schools, versus 10.4 students per outbreak at public schools.

Only 30% of charter school students who contracted chickenpox at school were vaccinated, researchers found, while half of public school students in school outbreaks were vaccinated.

“If these outbreaks could be prevented through vaccination, the burden of disease among charter school students could decrease,” the study states. “Continued education should be offered to the public regarding the efficacy of vaccination against infectious diseases to increase vaccination rates and protect of the health of all Utahns, specifically those most vulnerable to vaccine-preventable diseases like varicella.”

Varicella is another term for chickenpox.

Vaccinations are not 100 percent effective in preventing chickenpox; about 69% of students who contracted chickenpox were vaccinated, the report states. But symptoms were mild in most students who were vaccinated, and more than twice as likely to be severe in students who were not.

Nonmedical vaccine exemptions have been rising in Utah schools. From 2011 to 2016, nonmedical exemption rates in Utah schools increased from 3.8% to 5.1%., with public school exemption rates rising from 3.4% to 4.7% and charter school rates rising 8.4% to 9.4%.