A greater percentage of Maine kindergarteners entered school last year without being fully vaccinated, according to new data released as the state faces a surge in whooping cough cases and its first measles case in decades.

Five percent of kindergarteners, or about 620, were exempted by their parents from immunizations during the 2016-17 school year, according to updated data from the Maine Center for Disease Control and Prevention. That’s up from 4.5 percent the prior school year.

The vast majority of parents who opted against vaccination — 90 percent — cited philosophical objections. Their numbers increased for the first time since the 2013-14 school year, reversing a trend that had given public health advocates hope of waning skepticism about vaccines.

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Students are generally required to get shots to attend school, but Maine is among more than a dozen states that allow parents to exempt their children from school-required immunizations based on their philosophical beliefs or for medical or religious reasons.

Most Maine parents still vaccinate their children. But health experts warn that at least 95 percent of the population must be vaccinated to maintain “herd immunity,” when enough people in a group are vaccinated to prevent the spread of disease, even to unvaccinated individuals.

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Dr. Laura Blaisdell, a Yarmouth pediatrician who researches how parents make decisions about immunization, said as long as Maine law permits parents to opt out, the exemption rate will continue to rise.

“I’m not surprised…People will do what we require of them in our communities, so if we don’t have strong laws that mandate vaccination, then people will do what they want to do,” she said.

She cautioned that the opt-out rate is imprecise, capturing both parents who object to one vaccine and those who refuse them all. Some vaccinations are more critical to maintaining a community’s health, such as those that protect against whooping cough or measles, versus Hepatitis A, for example, she said.

“When we talk about exemptions, we’re talking about all vaccines,” Blaisdell said. “It’s kind of like saying all of Africa has giraffes. That’s not true. Not all of Africa has giraffes and not all vaccines are of dire public health concern.”

A Bangor Daily News analysis of the data from the 2014-15 school year identified several trends that continued to hold true during the last school year, the updated figures show. Along the coast, parents opt out of vaccines in greater numbers than in northern and central Maine. Parents who send their children to the private and charter schools sprinkled across Maine are also more likely to refuse immunization.

The number of private schools reporting data to the state doubled, to 46 last year from 23 in 2015-16. That likely accounts for at least part of the increase in the exemption rate, according to Maine CDC.

It also could help to explain why the kindergarten vaccination rate against measles, mumps and rubella dipped by 0.2 percent last year, officials said.

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That’s particularly concerning given that last month Maine confirmed its first cases of measles in 20 years. While health officials said the risk was limited to people who visited several locations in Franklin County during mid-June, measles is making a comeback in some communities across the country and in Europe. Just this week, New Hampshire health officials warned that an individual with measles may have exposed other visitors at the popular Hampton Beach.

Maine is also facing a spike in cases of whooping cough, another highly contagious disease that’s largely preventable with vaccination. Through June 30, the state recorded 227 cases of whooping cough, or pertussis, this year. That’s nearly double the 117 reported cases during the same period in 2016. Rates were highest among school-aged children in Cumberland, Kennebec, Oxford, Waldo and York counties.

Especially worrisome is that 10 of those cases were among infants under 6 months old. Pertussis is dangerous for babies — who don’t typically exhibit the characteristic “whooping” sound as they gasp for air — because it can rob them of oxygen, leading to brain damage and even death.

“If a certain number of newborns get pertussis, then we’re going to see some infant deaths, which is horrifying to say, but it is the reality,” Blaisdell said.

Children too young for the pertussis immunization or who haven’t built up enough immunity often catch the disease from a loved one who was never vaccinated or failed to stay current with booster shots.

Pertussis illustrates how allowing parents to opt out of vaccination puts others at risk, said Blaisdell, who has treated cases of the illness in her practice. Even people who are vaccinated against pertussis can catch it if too many other people in their community skip the shot, she said.

“Therein lies the crux of this opt-out concept, that no longer can I protect my child if I choose to vaccinate,” Blaisdell said.

Maine lawmakers considered legislation in 2015 designed to make it more difficult for parents to refuse vaccination, but Gov. Paul LePage vetoed the measure.

In Blaisdell’s practice, many of her patients’ parents choose to vaccinate, and many others don’t, she said.

“Our public structures like schools, as difficult as is it to say, they need to be safe for all children and all teachers. I don’t see any way around it without mandating that the kids who go to those schools are appropriately vaccinated,” she said.

I'm the health editor for the Bangor Daily News, a Bangor native, a UMaine grad, and a weekend crossword warrior. I never get sick of writing about Maine people, geeking out over health care data, and...