Two children at Rowe School in Yarmouth have been diagnosed with chickenpox in the past two weeks, prompting authorities to temporarily exclude five unvaccinated students from the elementary school.

Superintendent of Schools Andrew Dolloff said Tuesday that because of the chickenpox cases, the five unvaccinated students would be excluded from school for 16 calendar days, although two of those students could return to school sooner.

Chickenpox is a highly contagious disease, but there’s a vaccine for it that has been available since the 1990s. While children are required to get the chickenpox vaccine and other immunizations before attending school, Maine permits parents to opt out of vaccinations by signing a form saying they object on philosophic or religious grounds.

“We need to do this to protect them and others,” said Dolloff, explaining that Yarmouth is following rules of the Maine Center for Disease Control and Prevention. When health and public school officials determine that a public health threat exists, they can exclude unvaccinated students from school.

With the two cases, Rowe School is on the cusp of being considered an outbreak, which is defined by the Maine CDC as three or more cases of infectious diseases at any one location. Through Sept. 30, Maine had 149 cases of chickenpox, the highest rate in New England, according to the U.S. Centers for Disease Control and Prevention. New Hampshire, with nearly the same population as Maine, reported one case, while Connecticut, with about three times Maine’s population, had 78 cases.

Dr. Laura Blaisdell, a Yarmouth pediatrician, said chickenpox is not a mild childhood disease and can be dangerous. In severe cases, children can be sick for weeks, hospitalized with encephalitis or skin infections. The disease can be deadly for those who are immune-compromised as a result of undergoing cancer treatments or other conditions.

The chickenpox virus – varicella zoster virus – can resurface as shingles in middle-age people or seniors who were not vaccinated and previously contracted the disease.

Dolloff said of the five children who will be excluded from school two have had their first shot but are missing a booster shot. He said as soon as they receive their required booster shot vaccination, they will be allowed to attend school. The other three children will miss school for the full 16 days because they haven’t received their first shot.

Dolloff said because the 200-student school has a high vaccination rate this year – less than 2 percent have opted out of required vaccinations – disruption to the school will be minimized. In the 2015-16 school year, Rowe School’s non-medical opt-out rate was 3.6 percent, almost matching the state average of 3.7 percent, according to Maine CDC data.

Maine has one of the highest kindergarten opt-out rates in the nation, but vaccination rates have improved in recent years.

There are pockets of vaccine refusal at some Maine schools, with some schools having opt-out rates that reach 20 percent or higher. Fiddlehead School of Arts and Science in Gray, Kennebunkport Consolidated School and Hancock Grammar School, for example, all reported opt-out rates of 20 percent or higher for kindergarten or first grade in 2015-16. The 2016-17 school-by-school opt-out rates will be publicly available next spring.

If an outbreak occurred at one of the schools with numerous exemptions, dozens of students would be required to miss school for 16 calendar days.

“You don’t want students to be missing school, and 10-12 school days is a significant part of the academic year,” Dolloff said. “Kindergartners and first-graders have rapidly developing brains and need to be in school.”

Blaisdell said removing unvaccinated students from school is “exceptionally disruptive to the school. It’s an unmeasured cost of not protecting the population with vaccines.”

Maine’s overall non-medical opt-out rate for kindergarten students declined from 3.9 percent in 2014-15 to 3.7 percent in 2015-16. State-by-state results for 2015-16 will be released by the U.S. CDC this fall.

Maine was fifth-worst for vaccine coverage in the 2013-14 school year, when kindergarten opt-outs reached 5.2 percent. Typically, the national median for opt-outs is about 2 percent or less.

A 2015 bill that would have made it more difficult for parents to opt out of vaccines for their children failed after the Maine House fell five votes short in an attempt to override a veto by Gov. Paul LePage.

While Yarmouth school officials are talking publicly about the chickenpox cases, a proposed rule change by the Maine CDC would, if approved, make it easier for the state agency to deny public records requests asking to disclose the locations of outbreaks. The Portland Press Herald and a number of health organizations – including MaineHealth, the parent company of Maine Medical Center, and the Maine Medical Association, an advocacy group that represents physicians – have opposed the proposed rule change, which is pending a review by the Maine Attorney General’s Office.