Omer and colleagues surveyed 551 doctors. They found that more recent graduates were 15% less likely to believe that vaccines are effective, compared with older graduates.
Younger doctors were also more likely to believe that immunizations do more harm than good, Omer tells WebMD.
And they were less likely to believe that measles, mumps, rubella (MMR), polio, and chickenpox vaccines were safe when compared to older doctors, he says.
"We picked up subtle, but important differences," Omer says. But most doctors still strongly support vaccines.
As an example, 81% of the doctors, regardless of age, agreed that "vaccines are one of the safest forms of medicine ever developed," he says.
But each increase of five years in the year of graduation was associated with 20% lower likelihood a doctor believed that statement was true.
Eight percent of doctors overall agreed that "children get more immunizations than are good for them." But each increase of five years in the year of graduation was also associated with 20% increased odds a doctor believed that was true.
The findings are significant "because the most important source of information on vaccination is doctors," says Bruce Gellin, MD, director of the National Vaccine Program Office in Washington, D.C. He moderated a news briefing to discuss the findings.
The study wasn't designed to examine why age might affect beliefs on vaccination. Gellin's theory: Like young parents, young doctors are not familiar with some of the infectious diseases that have been virtually wiped out by immunization programs.
"As familiarity with a disease goes away, they're only hearing about the vaccine. That often isn't in sync with what the vaccines are designed to do," he says.
Omer stresses that parents shouldn't choose a pediatrician based on age. "Simply ask their beliefs on vaccination if you have concerns," he says.
Families 'Fired' for Refusing Vaccines
The second study involved 695 pediatricians from nine Midwestern states who filled out an online survey.
Overall, 21% of the doctors said they discharged families who continued to refuse all vaccines for their children.