New research by the Centers for Disease Control and Prevention (CDC) reveals that about a quarter of all U.S. children are out of compliance with vaccination guidelines.

The CDC researchers found that among children between 18 months and their 3rd birthday, 28 percent did not meet vaccination recommendations. The findings were based on a 2005 government survey including 17,563 US children in that age group.

The study reveals that the problem is not just that some parents don’t get their kids vaccinated at all, it also lies in the timing of vaccinations and the tendency to miss doses. For example, missed doses accounted for about two-thirds of those not in compliance. The rest got them at the wrong or too soon after a previous dose to be considered completely active.

When the researchers factored all those scenarios into the equation, they discovered that only 72 percent of kids are in total compliance with the guidelines, which means a 9 percent lower than previous figures. According to the CDC, most children in the U.S., by age 3, must have shots against at least 14 diseases including polio, influenza, hepatitis and chicken pox.

“Parents and providers need to do a better job communicating so that children receive all their vaccines on the recommended schedule. The schedule was designed to be safe and effective to prevent disease in their children,” said Elizabeth Luman, an epidemiologist at the CDC's Center for Immunization and Respiratory Diseases who led the study.

”We didn't look specifically at the implications on potential disease outbreaks. But we do know that doses that are given too early or too close together are not as effective as doses that are given the proper spacing and the proper age,” she added, according to Reuters.

Dr. Luman said she understands the difficulty parents have in meeting strict vaccination schedules, but, at the same time, she emphasizes the importance of making a good effort to get kids in for their vaccinations on time.

“I have two kids, and from a parent’s point of view, it can be hard, logistically, to come in when scheduled. But I know how important timely vaccination is for the health of my children and my community,” she said.

The findings of the study appear in the June issue of the American Journal of Preventive Medicine.