The percentage of parents who refused or delayed vaccinations for their children rose sharply in the past decade, a study presented at a medical conference today showed.
Thirty-nine percent of parents refused or delayed vaccinations for their kids in 2008, up from 22 percent in 2003, according to the study by the Centers for Disease Control and Prevention, the University of Rochester and the National Opinion Research Center.
Parents refused or delayed vaccinations for various reasons, including the health of the child, the belief that recommended vaccines were excessive, questions about their effectiveness and concerns about possible side effects such as autism -- although there's no scientific link.
Such concerns created delays that worried ABC News senior health and medical editor Dr. Richard Besser.
"The issue with hesitance or delaying vaccinations is that the period that you are at risk increases," he said. "If you are in a community where a lot of parents are refusing vaccination, delaying vaccination may pose a risk."
Dr. Mark Sawyer, a pediatrician at Rady Children's Hospital in San Diego, agreed, saying in March that "the risk from the diseases vaccines prevent is what parents should be concerned about."
Besser also said the increased number of vaccines available by 2008 should be taken into consideration.
"While the percentage of parents delaying and refusing vaccines has gone up, we offered more vaccines in 2008 than in 2003," he said. "So there were more opportunities to delay or refuse getting them in 2008 than there were in 2003. It's important to note that vaccine coverage overall has increased during the study period."
Based on the study, which was presented at the 2010 Pediatric Academic Societies' Annual Meeting in Vancouver, Canada, Besser said 0.6 percent of children between ages 19 months and 35 months remain unvaccinated.
"While some children are not vaccinated by the recommended age, most of them do end up getting all of their vaccines," he said.
Although the percentage of parents refusing or delaying vaccinations rose, CDC data indicated that vaccination completion of the primary vaccines by age 2 increased overall between 2003 and 2008, the year for which the most recent data is available.
Today's study may indicate that more parents are spacing out vaccines and possibly refusing newer vaccines, Besser said.
The risk of letting a child play with an unvaccinated child is small but real, Besser said.
"Not all vaccines are 100 percent effective," he said. "Unvaccinated playmates may put you at risk if your vaccine did not provide complete protection. ... It depends on the infection you are talking about and how it is transmitted.
"Just realize that as the number of vaccine refusers rises, there is risk."
When he was a practicing pediatrician, Besser said, he often told mothers who refused vaccinations to find another pediatrician.
"I regret that now," he said. "Now, I try to develop an open relationship and provide parents with information so that they can make an informed decision. In the end, it's the parent's decision.
"I know of nothing we do in pediatrics that has as much proven value as vaccinations -- not all parents agree," he said.
PBS's "Frontline" recently tackled the vaccine debate in a new documentary called "The Vaccine War." Click here to learn more from its website.