naumoid via Getty Images Pediatricians perceive changes in parents' vaccine-related views in the past several years.

If ever there was an idea that doctors, researchers and public health experts are in agreement upon, it’s that vaccines are safe and strongly recommended. The American Academy of Pediatrics supports immunizing children. So does the Centers for Disease Control and Prevention. The vast majority of parents in the United States clearly do as well, as evidenced by national vaccination rates that have remained relatively stable ― and high.

Yet according to a new study published in the journal Pediatrics on Monday, pediatricians say they’ve seen a shift in parents’ concerns about childhood vaccines in the past decade ― and not necessarily a good one. Doctors report that they’re seeing more caregivers who are looking to delay vaccines, or refusing them altogether, suggesting the anti-vaccination movement may still have legs.

The researchers compared surveys of random samples of practicing pediatricians administered in 2006 and 2013. Both years, roughly 600 doctors responded.

The 2006 survey did not ask about vaccine delays, so the researchers were unable to track trends overtime. However, the 2013 survey found that nearly 88 percent of pediatricians had been asked by parents to hold off on at least one vaccine within the last year. Most parents were worried about their child’s discomfort, or believed the vaccines would be too much for their immune system all at once, pediatricians reported. There's sufficient evidence, however, that delays can be harmful and vaccines do not “overload” the immune system, as they contain only a fraction of the antigens (substances like viruses, bacteria, chemicals or pollen, for example) that children encounter every single day.

In the 2006 survey, nearly 75 percent of pediatricians said they’d seen parents who’d refused at least one vaccine in the past year. By 2013, however, that had grown to 87 percent.

In that time, the reasons why parents refused changed, pediatricians said, and a growing number of parents seem to feel vaccines are simply unnecessary.

“The concern that vaccines are necessary [being given] as a reason for refusal increased significantly from 63 percent [in 2006] to 73 percent [in 2013], which I found very interesting,” said study author and pediatrician Dr. Catherine Hough-Telford, with the University of Alabama, Birmingham.

“Most of the parents making the decisions about vaccines for their children have no first-hand knowledge of children getting sick and dying from measles, from congenital rubella, even pertussis,” Hough-Telford continued. “Even a generation ago, these bacteria and viruses were killing babies and children.” Whopping cough, for example, was one of the most common childhood diseases in the U.S. in the 20th century and a major cause of childhood mortality. And in the 1950s -- a decade or so before a vaccine for measles was available -- between 3 and 4 million people were infected with that infectious disease every year.

The new survey was administered before the well-publicized 2015 measles outbreak linked to an amusement park in California, Hough-Telford noted, adding that it would be interesting to see if parents’ feelings have changed since then.

The number of parents who refused vaccines because of fears about autism did appear to drop between the two surveys; however, it is clearly still a force. In 2006, 74 percent of pediatricians cited it as a reason why parents refused vaccines. In 2013, 64 percent did.

But rather than finding these overall trends troubling, Hough-Telford said she felt optimistic. Now that pediatricians have a clearer sense of parental concerns, they can work harder on education.

“It’s an opportunity for us, as clinicians, to help parents understand these vaccines and the diseases they prevent,” she said. “While it’s definitely something to take notice of, I think we should see it as an opportunity for change.”