Some lawmakers and a statewide pro-vaccine group have vowed to renew efforts to strengthen Maine’s vaccination laws, hoping to capitalize on increased public education campaigns touting the benefits of vaccines.

Studies show states that have laws that make it more difficult for parents to opt out of vaccines have higher vaccine participation rates.

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

Mainers are increasingly skeptical about the safety of vaccines, as the percentage of parents opting out of vaccines has increased since 2004, entirely because of parents objecting on philosophical grounds, according to Maine Center for Disease Control and Prevention statistics.

Maine 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-vaccine forces admit they will face a tough challenge with a balky Legislature, as lawmakers return for the 2015 session in January. A bill that would have weakened the state’s vaccination laws supported by anti-vaccine advocates passed in 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 vaccine usage.

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 and the threat that the diseases will return motivated her to find more effective solutions. A modest bill by Graham that would have required schools simply to hand out pro-vaccine literature to parents failed last year.

“There’s a sense of urgency now,” Graham said, and perhaps a dawning realization by pro-vaccine parents that people who choose to leave their children unvaccinated increase the risk to others. If more people are unvaccinated, “herd immunity” breaks down and outbreaks can occur, scientists say, even among those who had taken their vaccines.

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 vaccine advocates, including the Maine Immunization Coalition, in the upcoming weeks to forge a strategy for the 2015 legislative session.

Even though some parents doubt the wisdom of using vaccines, advocates point out that most parents support vaccines, 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 vaccines.

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

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

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

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

The extra hurdle to obtain a philosophic exemption appears to be working in Washington state, according to public health advocates there and CDC statistics.

In Washington, the kindergarten opt-out rate declined from 4.2 percent in 2012 to 3 percent in 2013, the first school year in which the 2011-approved law was implemented fully.

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 about vaccines 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. Vaccine advocates say listing the ingredients needlessly scares parents.

Boland said she’s wary of vaccines and 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 tried 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 in the Legislature in 2015, she said she believes another lawmaker will take up the bill.