“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 non-vaccinators. 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.