AUGUSTA — The Maine Senate voted Thursday to pass a bill that would end philosophical exemptions to childhood vaccinations but would continue to allow parents to cite religious objections to vaccines.

If the religious exemption survives additional votes in the House and Senate, it could undermine efforts to increase vaccination rates among Maine children that reduce the risks of infectious disease outbreaks.

The razor-close, 18-17 vote to preserve religious exemptions for vaccinations puts the bill at odds with a version passed last week by the Maine House, further complicating the path ahead for one of the most contentious and closely watched issues of this year’s legislative session.

The bill now heads back to the House, where lawmakers will debate whether to accept the religious exemption or force a potential showdown with the Senate on the change.

Under current Maine law, parents are able to obtain a medical exemption or sign a statement citing philosophical or religious grounds for opting out vaccinating children for measles, mumps, pertussis and other infectious disease. That has resulted in Maine registering one of the nation’s lowest vaccination rates for children entering kindergarten and the country’s highest rate of pertussis or whooping cough.

The Senate initially voted 20-15 to give initial approval to a bill, L.D. 798, that would end both philosophical and religious exemptions, effectively mandating that almost all children be vaccinated in order to attend schools.

But four Democrats — Sen. David Miramant of Camden, Sen. Erin Herbig of Belfast, Sen. Louis Luchini of Ellsworth and Sen. James Dill of Old Town — then joined the chamber’s 14 Republicans to change the bill to preserve religious exemptions.

Miramant, who was the only Democrat to oppose the original bill, warned that ending both exemptions would mean an estimated 9,000 children could be prohibited from attending school because they lacked all mandated vaccinations.

“(Their parents) are not going to rush to get this done so their kids can go to school,” Miramant said. “I’ve had many contacts with people who would leave this state because there are plenty of places you can go that will honor your philosophical or religious exemptions.”

Supporters, meanwhile, warned that allowing religious or philosophical exemptions puts at risk children who are immuno-compromised as well as infants susceptible to disease because they are too young for vaccinations.

“At the end of the day, this bill is about making sure our public schools are safe, healthy environments for our young people to learn and grow,” said Sen. Rebecca Millett, D-Cape Elizabeth.

Like many states around the country, Maine has seen an increase in the number of parents who are opting not to vaccinate against a host of infectious diseases because of concerns about side-effects from vaccinations or for religious reasons. But public health officials counter that much of that concern is based on misinformation and warn that the growing number of unvaccinated children is compromising the “herd immunity” that prevents the spread of infectious diseases.

The bill faces additional votes – and likely debate – in both the House and Senate. Under both of the competing versions approved by the two chambers, parents concerned that a vaccine could harm the health of their child could still seek a medical exemption from their doctor or could seek authorization to change the vaccination schedule.

Three other states – California, Mississippi and West Virginia – have banned all non-medical exemptions that allow parents to forgo school-required vaccines for their children.

During the 2018-19 school year, 5.6 percent of Maine children entering kindergarten had non-medical exemptions for immunizations, state statistics show. That means many Maine schools have dropped below the 95 percent vaccination threshold thought to offer “herd immunity” protection to prevent the spread of infectious diseases because so much of the population is immune.

More than 90 percent of non-medical exemptions in Maine during the 2018-19 school year were for philosophical reasons, with just 7 percent citing religious objections. Opponents of Miramant’s amendment said it will merely prompt more parents to cite religious rather than philosophic objections.

Indeed, Vermont saw a spike when policymakers removed the philosophic exemption during the 2016-17 school year. Religious opt-outs from vaccinations jumped from 0.9 percent in 2015-16 to 3.7 percent in 2016-17, according to Vermont state statistics.

Luchini, the Ellsworth Democrat who supported keeping religious exemptions, pointed to Harvard and Stanford universities as two institutions that allow students to cite religious beliefs when enrolling without the required vaccinations. Luchini said maintaining that exemption could be important to Maine colleges and universities as they seek to recruit international students from countries with differing vaccination policies.

“There are only three other states in the country that don’t offer religious exemptions, and that was part of my thinking,” Luchini said. “And I have heard from a lot of parents who want that exemption.”

Vaccinations have emerged as one of the most emotional issues of the 2019 legislative session, spurred by a growing number of outbreaks of measles, whooping cough and other diseases across the country. Hundreds of people on both sides turned out for a roughly 13-hour public hearing on the exemptions bill in March.

On Thursday, advocates on both sides of the issue clogged the hallway as well as the Senate chamber and audience gallery in anticipation of the vote. Senators debated for more than an hour, occasionally sharing their own personal experiences with vaccinations.

Sen. Robert Foley, R-Wells, recounted how his 2-month-old daughter died just 36 hours after receiving her first set of vaccinations. Foley said he and is wife are convinced that the immunization shots “played a significant and vital role in our daughter’s untimely and unfortunate death.”

Foley said her doctor wanted to have the vaccine serums tested for imperfections, but state officials rebuffed those efforts. As a result, Foley’s daughter’s death was attributed to “sudden infant death syndrome.”

The couple had their two subsequent children vaccinated for most — but not all — diseases and those vaccines were administered after they were 6 months old and were spaced out to avoid multiple injections. Under the original version of the pending bill, however, his children would have been prevented from attending any Maine schools because they lacked one vaccination.

“There must, there must be a better way for us to protect all of Maine’s children other than segregating a portion of that population, as this bill proposes,” Foley said.

But Democratic Sen. Linda Sanborn, a retired family physician from Gorham, recalled her many conversations explaining the risks and benefits of vaccinations to parents whose children were in her care. Each of those decisions was made on an individual basis after consultation, Sanborn said.

But health care providers are increasingly alarmed by an anti-vaccination movement in the U.S. and around the world that she said is based on misinformation. She pointed out that the bill would still allow exemptions based on the “professional judgment” of health care professionals caring for those children.

“L.D. 798 is not about forcing parents to do something against their will or taking away choice,” said Sanborn, a Democrat. “It is about how the choices we make have consequences for ourselves and for others.”

Staff Writer Joe Lawlor contributed to this report.