Whooping cough made a comeback in California last year, which researchers have linked to vaccine refusals. And with new measles outbreaks in Southern California, New York and British Columbia, the debate over vaccination is also spreading.

Forty-eight states allow parents to sign a vaccine exemption form — only West Virginia and Mississippi don't. California now requires a doctor's signature on the school form, but parents are still able to find doctors who will sign.

It can be a touchy subject, and even some physicians are unsure of how to approach parents who don't want to vaccinate their children. Still, health professionals and pro-vaccine parents are trying new ways to share their message.

Matt Willis, a public health officer for Marin County, says if pediatricians know why parents aren't vaccinating, they can come up with responses to try to change parents' minds.

He helped design a survey to figure out what parents are worried about. They canvassed parents in Marin County, just north of San Francisco, the site of the whooping cough cases.

"Some of the themes that came out of the survey [were] ... preference for natural immunity over immunity conferred by vaccines; children perceived as low risk for some vaccine-preventable diseases; and lack of trust for the health care system or pharmaceutical industry," he says.

Doctors' Approach

Physicians use that kind of information in different ways. Michael Yamaguchi, attending a presentation by Willis, says he gives parents articles from scientific journals.

"I hand them the article and I say, 'Look, if you're going to disbelieve this, you have to say these eight authors [and] the entire editorial board are all in somehow collusion to create some sort of data that's untrue," he says.

Other doctors say changing minds is not easy.

"I think there are those parents that come in with their mind made up, and there's nothing you can say to sway them," says Lisa Leavitt.

A study at Dartmouth College supports that theory. Political scientists surveyed nearly 1,800 parents about the vaccine for measles, mumps and rubella (MMR). What they found was that the more skeptical parents are about vaccines, the less likely they are to listen to public service ads or to their pediatricians.

Marin County pediatrician Nelson Branco hasn't given up on convincing nonvaccinators. He gave parents an ultimatum in 2012: Vaccinate your toddler against measles, mumps and rubella by the time the kid is 2 years old, or find a new pediatrician.

And for some people, it worked.

"There were many families who were on the fence about vaccines who chose to get the MMR vaccine and stayed in our practice," he says. "There were very few families that left our practice."

Fewer than 20 families left, and about 150 families chose to vaccinate.

A Mom's Plea

Mother Sonia Green has also taken up the cause of convincing parents to vaccinate. Her three boys have an immune disorder called XLA. Ten-year-old Holden and his two brothers are basically "walking around with half their immune system missing," Green says.

Because of their condition, the boys can't be vaccinated. If they were, Green says, the best-case scenario would be that the vaccination would do nothing. The other scenario is that they wouldn't develop the immune response from the vaccine and would instead become very sick.

If enough people in a community are vaccinated, then even those who didn't get vaccines are likely to be protected. If other children aren't vaccinated, kids like the Green brothers are at greater risk.

Last spring, Holden was exposed to something that for another kid might not have been a problem, Green says. But for Holden, it caused a skin infection that required him to be in the hospital for about a week.

Green wrote a blog post explaining why vaccinations are important to families like hers. She says she has talked to other parents about the issue and that some decided to vaccinate after hearing her story.

Part of what keeps Holden and his brothers healthy, Green says, is that she lives in a community where most people are vaccinated. But she says she's ready to pull her kids from a school or situation where she knows most people around her kids are not vaccinated.

"To me, they're gambling with my kids' lives when they don't vaccinate their kids," she says.

Correction: April 7, 2014 12:00 am — In the audio of this story, we incorrectly say that 10 children in Marin County died of whooping cough. The children were in California but not Marin County.

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