Some lawmakers and a statewide pro-vaccination group say they will renew efforts to strengthen Maine’s vaccination laws in hopes of reducing the percentage of Maine children who aren’t being inoculated against measles, whooping cough and other diseases.

States with laws that make it more difficult for parents to choose not to get their children vaccinated have higher participation rates, studies show.

And states with weaker vaccination laws have seen a return of diseases that had been mostly eradicated for decades, such as the major pertussis outbreak in California in 2010. Since then, California, Washington and a few other states have tightened vaccination laws.

The percentage of Maine parents who don’t get their children vaccinated has increased since 2004, and the entire increase is among parents who object on philosophical grounds, according to Maine Center for Disease Control and Prevention statistics.

Maine now has one of the highest kindergarten vaccination opt-out rates in the nation, at 3.9 percent, and public health advocates worry that diseases such as whooping cough and measles will infect thousands if opt-out rates don’t decline. In 2012, Maine had more than 700 cases of pertussis – whooping cough – the most since the 1960s.

Maine’s pro-vaccination forces admit they face a tough challenge in the Legislature when lawmakers return for the 2015 session in January. A bill that would have weakened the state’s vaccination laws was passed by the House last year, but failed in the Senate.

“It’s almost like the Legislature doesn’t understand the importance of vaccines,” said Rep. Ann Dorney, D-Norridgewock. Dorney said she would support any efforts to boost vaccination rates.

Rep. Anne Graham, D-North Yarmouth, a pediatric nurse practitioner, said a story in the Maine Sunday Telegram about the state’s high opt-out rate motivated her to find a solution. A modest bill by Graham that would have simply required schools to hand out pro-vaccination literature to parents failed last year.

“There’s a sense of urgency now,” Graham said, and perhaps a dawning realization by pro-vaccination parents that people who choose not to have their children vaccinated are creating a risk to others. If more people are unvaccinated, it is easier for diseases to spread, scientists say, even among those who had been vaccinated but who had not developed immunity to certain diseases.

Studies that seemingly linked vaccines to autism in the 1990s have since been debunked, but anti-vaccination sentiment persists and in some ways has grown. Skeptics often cite a large body of online literature that claims vaccines contain toxic elements.

Graham said she will be huddling with vaccination advocates, including the Maine Immunization Coalition, in the upcoming weeks to forge a strategy for the 2015 legislative session.

Even though some parents are skeptical of the benefits, advocates point out that most parents support vaccination, and tapping into that population is key.

“We need to figure out how to cultivate those pro-vaccine voices,” said Cassandra Grantham, executive director of the Maine Immunization Coalition, a group of medical professionals that advocates for vaccination.

The No. 1 target? The philosophical exemption, and Maine’s laws requiring parents simply to sign a form to opt out for philosophical reasons.

“Eliminating the philosophic exemption is the ultimate goal,” Grantham said.

Twenty states allow parents to opt out of vaccinations on philosophical grounds. Almost all states also permit religious opt-outs, but religious exemptions are more rarely used, according to statistics by the U.S. Centers for Disease Control and Prevention.

Grantham said trying to get rid of the philosophical exemption may be too difficult right now, considering the political climate and the Legislature’s votes last year. But she said it’s time to discuss options such as requiring the signature of a medical professional to opt out on philosophical grounds.

The extra hurdle to obtain a philosophical exemption appears to be working in Washington state, according to public health advocates there and federal CDC statistics. The kindergarten opt-out rate there declined from 4.2 percent in 2012 to 3 percent in 2013, the first school year that the 2011-approved law was fully implemented.

Dr. Peter McGough, a Washington family physician and the chief medical officer of the University of Washington’s Neighborhood Clinics, said that from what he’s seen in his office, parents who were skeptical of vaccination can be persuaded after talking with a doctor.

“Sometimes all the information they’re going on is what they’re reading on the Internet,” McGough said.

He said Washington’s public health groups and politicians came to realize that the laws were too weak.

“We had these huge outbreaks of pertussis and measles,” McGough said. “We determined that the laissez-faire approach was really affecting public safety.”

In 2013, a Maine bill that would have required that parents be given a list of ingredients in vaccines and informed about how they could opt out passed 82-61 in the House, despite a recommendation against the law by the Health and Human Services Committee and opposition by the medical community. The bill, sponsored by Rep. Andrea Boland, D-Sanford, failed in the Senate, and no compromise bill was forged in the conference committee. Vaccination advocates say listing the ingredients needlessly scares parents.

Boland said she’s wary of vaccines, and she believes studies that cast doubt on their safety.

“I don’t want to tell any parent whether to vaccinate or not,” Boland said. “Information is being withheld from parents.”

Boland said she attempted to get her bill passed a few times, and each year it’s “gained momentum.” Even though Boland has served the maximum terms allowed and won’t be serving in the Legislature in 2015, she said she believes another lawmaker will take up the bill.