A North Carolina school where a high concentration of families claim religious exemption from vaccines is facing the state’s worst chickenpox outbreak in more than 20 years.

The chickenpox outbreak has affected 36 students at Asheville Waldorf School, health officials with Buncombe County said. The outbreak ranks as North Carolina’s largest since a chickenpox vaccine became available more than 20 years ago, the Asheville Citizen Times reports.

The Asheville Waldorf School has one of the highest rates in the state of families who opt out of vaccines based on religious beliefs, according to data from North Carolina’s Department of Health and Human services. Of the 28 children enrolled in kindergarten at the school during the 2017-2018 school year, about 19 claimed religious exemption from vaccines — a higher rate of exemptions than all but two other schools in the state, according to the Citizen Times.

Buncombe County medical director Dr. Jennifer Mullendore drew a link between the widespread chickenpox update and the low records of immunization.

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“We want to be clear: vaccination is the best protection from chickenpox,” Mullendore said in a statement. “Two doses of varicella vaccine can offer significant protection against childhood chickenpox and shingles as an adult. When we see high numbers of unimmunized children and adults, we know that an illness like chickenpox can spread easily throughout the community — into our playgrounds, grocery stores, and sports teams.”

While North Carolina requires immunizations for all kindergarten-age students, including the two-dose chickenpox vaccine, it does allow for medical and religious exemptions. Parents who want to claim religious exemptions for their children have to describe their religious objection to immunization in a written statement given to schools and other child care programs in lieu of an immunization record.

A statement from Asheville Waldorf said the school follows immunization requirements.

“Our school strictly follows immunization requirements put in place by the North Carolina State Board of Education. As an associate member of the Association of Waldorf Schools of North American and like all other Waldorf Schools, we are compliant with national, state and local laws,” the statement said. “We also recognize that a parent’s decision to immunize their children happens before they enter school. At Asheville Waldorf School we support our families, we love our students, we love our city and we are grateful that our community is strong during challenging times.”

School officials did not immediately respond to requests for comment.

The chickenpox outbreak comes amid a startling growth of the number of unvaccinated children. Anti-vaccination sentiments have taken off among some communities in recent years, spurred by the myth that vaccines are linked to increased rates of autism that dates back to a now-debunked and retracted 1998 study. Despite evidence pointing to immunizations as an effective way to protect against diseases like chickenpox, the Centers for Disease Control and Prevention (CDC) said this year that the percentage of children with no vaccinations under the age of 2 quadrupled since 2001.

The CDC also found an overall increase in exemption rates for kindergarten-age children, with Oregon holding the highest median rate.

Write to Mahita Gajanan at mahita.gajanan@time.com.