When Maine’s voters head to the polls in the presidential primaries Tuesday, they also will cast a vote on an issue many physicians wish had never been politicized — a referendum to overturn a new law that would allow unvaccinated children to attend school only if they have received a waiver from a medical professional.

The new law, which would take effect in September 2021, aims to boost immunization among school-age children in a state where just over 5 percent of kindergartners are unvaccinated not only for medical reasons but because of their parents’ religious or philosophical beliefs. That puts Maine below the 95 percent threshold that public health officials say is necessary to stop the spread of preventable and sometimes deadly diseases like the measles.

The referendum was added to Tuesday’s ballot after opponents of the new law gathered sufficient signatures to trigger a vote. In many states, misinformation campaigns have raised fears about the alleged dangers of immunization, which extensive research has shown are unwarranted.

“Certainly, referendums are not my ideal method for determining public health policy,” said Laura Blaisdell, a pediatrician and vice president of the Maine Academy of Pediatrics, who said the new law had become necessary after efforts to educate parents in the exam room and in the community had failed “to stem the dangerous tide.”

“Our perspective is that it’s a massive overreach on the part of the state to take away parents’ rights,” countered Cara Sacks, campaign manager for Yes on 1. The group has found another boogeyman in “Big Pharma,” which Sacks blames “for driving the mandates.” She said she is “cautiously optimistic” that her grass-roots movement will win Tuesday.

The two have been locked in a battle over hearts and minds and ultimately the ballot box, appearing in town halls, on live TV and in radio talk shows.

The debate — and the forum in which it will be decided — has exposed the delicate relationship between the law and public health. Legislation has long helped normalize safe behaviors like wearing seat belts. But some supporters of immunization argue that stringent laws can be blunt instruments when applied to an issue like vaccines that plays on people’s fears, even if they are misguided.

“They risk creating a backlash,” said Daniel Salmon, director of the Institute for Vaccine Safety at the Johns Hopkins Bloomberg School of Public Health, motivating worried parents to look for other ways to avoid immunizations they mistakenly believe are harmful.

“Parents may not be right, but if that is what you believe, your choice is to home-school, move out of state or find a doctor to write a medical exemption,” Salmon said.

The problem that needs to be addressed, physicians say, is widespread misinformation. Salmon says that as many as one out of every three or four parents has concerns about the ingredients in vaccinations, the number of immunizations given at one time, and rumored links to autism that are not supported by science.

Maine’s law was passed last year amid heightened concern about measles outbreaks, following a drop in vaccination rates in several communities, including Eastern European immigrants outside Portland, Ore., the Somali community in Minnesota and ultra-Orthodox Jews in Brooklyn.

The highly contagious and sometimes fatal illness was eliminated in the United States in 2000, according to the Centers for Disease Control and Prevention. Between January and September of last year, 1,249 cases were reported, the highest annual number since 1992. Ten percent needed to be hospitalized.

New York passed legislation eliminating the religious exemption for public school students. Washington state chose a narrower approach — removing the personal belief exemption only for the measles, mumps and rubella vaccine.

The referendum in Maine comes amid fears about a new disease — covid-19, caused by coronavirus — for which there is not yet a vaccination and probably won’t be one for a year or more.

“Right now, unimmunized American children are at far greater risk of severe disease and death from measles than coronavirus,” said Ruth Karron, a pediatrician, professor at the Johns Hopkins Bloomberg School of Public Health and founding director of the Johns Hopkins Vaccine Initiative.

Vaccines are often victims of their own success, she said, explaining that parents who have no memory of the misery caused by polio or measles are sometimes reluctant to immunize their children. On the other hand, she said, people’s fears of the unknown can increase demand for a vaccine. In the wake of 9/11, amid worries about bioterrorism, people began requesting a smallpox vaccine, even though that particular vaccination can have serious side effects.

If the Maine law is overturned by popular vote, it would not only set back the state’s attempts to protect the population from common childhood diseases but highlight what some physicians see as the risk of mixing public health with politics.

“I’m very concerned about the politicization,” said Karron, because of the danger of clouding the scientific message.

“I really think that the public has a right to unfettered and clear communication from our best scientists,” she said. “That’s what it means to live in a democracy.”

“Political issues are divisive,” Salmon said. “In vaccines, we need almost everybody’s support. If we end up with 50 percent for and 50 percent against, we’ll have raging disease.”