The state of North Carolina in the southeastern US is having its worst outbreak of chickenpox in two decades, and it's all centered on a community where people claim religious exemptions to getting vaccines.

"This is the biggest chickenpox outbreak state health officials are aware of since the vaccine became available," said a North Carolina Department of Health spokesman.

Three dozen students at Asheville Waldorf School were diagnosed with the disease as of last Friday.  Since it tends to be pretty contagious, and since 110 of the school's 152 students have not received the vaccine for the varicella virus, more infections are likely.  And the littlest are the most at risk, as 67.9 percent of the school's kindergarteners had religious immunisation exemptions on file (.pdf link) in the 2017-2018 school year.

"The school follows immunization requirements put in place by the state board of education, but also recognizes that a parent's decision to immunize their children happens before they enter school," the school said in a statement. 

But health officials tied the outbreak to low immunization numbers.

"We want to be clear: vaccination is the best protection from chickenpox," said County Medical Director Dr. Jennifer Mullendore.  "When we see high numbers of unimmunised children and adults, we know that an illness like chickenpox can spread easily throughout the community - into our playgrounds, grocery stores, and sports teams."