Pediatricians face growing numbers of parents who question or reject vaccinations for their children. Now, public health experts are working on new ways to help these doctors hone their pitches to families.

Pediatricians need to step up their game, the researchers say, to counter a spigot of unscientific antivaccine material distributed over the Internet and elsewhere and help stem a rise in measles cases in the U.S.

On Monday, the Centers for Disease Control and Prevention plans to release updated figures on the current outbreak, which began at a Disneyland resort in December.

When her first child, Vivian, was born six years ago, Juniper Russo refused vaccines because she wanted to embrace a “natural parenting” culture, she said.

“I had clung to the idea that if I breast fed and fed my daughter natural, healthy food and let my daughter play outside that would keep her safe,” said the 27-year-old mother of two in Chattanooga, Tenn. Ms. Russo said she thought vaccines were part of an “unnatural” lifestyle that caused autism, alongside “junk food and TV and ultrasounds.”

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