No on Question 1 organizers (from left) Laura Blaisdell, Caitlin Gilmet, Peter Michaud and Deb Deatrich, celebrate their victory in Portland on Tuesday night.

AUGUSTA, Maine — A new Maine law tightening school vaccine requirements will go into effect after voters rejected a people’s veto challenge on Tuesday, making the state the fifth to bar parents from exempting children from vaccines for nonmedical reasons.

The measure backed by Democratic Gov. Janet Mills passed largely along party lines in the Legislature last year as a response to rising vaccine opt-out rates in Maine schoolchildren that reached the sixth-highest mark in the nation during the 2018-19 school year, according to the U.S. Centers for Disease Control and Prevention.

The “no” side led with 67.6 percent of votes when the Bangor Daily News and Decision Desk HQ called the race at 9:17 p.m. on Tuesday night with 22 percent of precincts reporting. Question 1 was the only issue on the statewide ballot alongside the Democratic and Republican presidential primaries on Tuesday.

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No on 1 campaign manager Bobby Reynolds said it was the backing of health care providers and groups representing pediatricians and hospitals alike that carried the day for their side.

“Mainers are practical folks who clearly listened to medical professionals,” he said. “At its core, this was a public health issue.”

Cara Sacks, the campaign manager for the yes side, cast the campaign’s defeat as the result of powerful lobbying from big pharmaceutical companies and bad initial guidance from Secretary of State Matt Dunlap’s office on the timing of the election during a Democratic presidential primary that provided a difficult environment for them.

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“We know how devastated you are right now,” she told supporters at a party in Augusta. “Our opponents will come to know that same feeling of loss one day, when their neighbors move, their children lose beloved classmates, businesses close or one day when they need the essential right to make their own medical decisions that they have now willingly handed over to an untrustworthy government.”

The law will take effect in September 2021 and apply to children and others attending public and private K-12 schools, colleges and universities and employees of nursery schools and health care facilities. The story that played out during the campaign was a microcosm of a larger national debate over vaccines.

The “no” side relied on scientific evidence that the health risks of vaccines are small and outweighed by the protective benefits of the majority of the population being vaccinated, which is referred to as “herd immunity.” Hundreds of the law’s opponents packed a legislative hearing on the bill last March making arguments against the bill ranging from religious and personal freedom to a debunked link between vaccines and autism.

Two groups opposing the people’s veto — Maine Families for Vaccines and a political committee run by the consulting firm Maine Street Solutions — spent $790,000 in the campaign to preserve the law. Pharmaceutical giants Merck and Pfizer spent $500,000 to oppose the question.

That added fuel to the argument for people’s veto backers that a “yes” vote was a rejection of “big Pharma.” The “yes” side gathered 79,000 signatures last year in a successful bid to put the question on the March ballot. Yes on 1 efforts were primarily funded by individual donations to the tune of $340,000.

Andrew and Carrie King, a Republican couple voting in Brewer on Tuesday, said they have two young granddaughters who are approaching school age and cited them as the reason they were voting to preserve the law.

“Every child should be vaccinated,” Carrie King said.

BDN writer Eesha Pendharkar contributed to this report.