Results of a newly-released study highlights a growing number of U.S. parents are opting not to have their children vaccinated according to health guidelines.

The study from the Kaiser Permanente Colorado Institute for Health Research found that nearly half of young people between the ages of 2 and 24 have either not followed the recommended vaccination schedule, or have not been vaccinated at all.

Common objections to following the recommended vaccine regime include concerns over the number of vaccinations, the age at which vaccinations start and a belief that other precautions or treatments would be better.

Based on her experience, CTV medical consultant Dr. Marla Shapiro believes the same trend has taken hold in Canada, too.

Many parents overwhelmed by long-held misconceptions further fuelled by the online chatter of social media are opting out, Shapiro said.

"There's this fear that's not based on evidence, or science," Shapiro told CTV News Channel, suggesting that anyone who delves into the facts about vaccines would find no reason to fear them.

And the consequence of skipping immunizations can be grave, she said.

Anyone who declines the vaccine for chicken pox, for example, might think they're only risking coming down with a highly contagious, albeit non-life-threatening illness.

But the reality, in Shapiro's view, is they risk coming down with one of the many more perilous complications of the disease.

"You can have... widespread complications that are not as common, but if they happen with a vaccine-preventable illness, it's just heartbreaking to see," she said. "I think we're getting complacent, and we're not relying on the science or the evidence."

From her medical practice, Dr. Marla's most commonly-heard flu vaccine misconceptions include:

  • The vaccine causes the flu
  • I can't get the shot because I'm allergic to eggs
  • I can't get the shot because I'm pregnant
  • I never get the flu anyway

None of them hold up to scientific scrutiny, Shapiro said, starting with the fear of infection from the live vaccine now given to children in a nasal spray.

"It's heat-sensitive and can't replicate in the lung," she said.

Pregnant and allergic individuals would likely suffer no ill effects either, she added, suggesting those candidates for the shot can consult with their doctor first.

And anyone relying on their own immune system to fight off infections aren't doing themselves -- or others they might come into contact with -- any favours.

"Maybe you'll do a good job and only miss a couple of days, but what about all the exposure that you bring to young children who we have seen get very ill... or an elderly individual," Shapiro said.

Results of the vaccine compliance study, based on data from the U.S. Vaccine Safety Datalink, are published in the latest edition of the medical journal JAMA Pediatrics.