TUESDAY, April 29, 2008 (HealthDay News) -- New numbers show that more than a quarter of American toddlers may be under-vaccinated.
The study of children aged 19 months to 35 months found that missed doses account for about two-thirds of non-compliance to official recommendations. However, miss-timed doses are also an issue, according to a study conducted by the U.S. Centers for Disease Control and Prevention (CDC) and published in the June issue of the American Journal of Preventive Medicine.
Immunization delays put children at risk for a variety of vaccine-preventable diseases such as measles, mumps and chicken pox. On the other hand, immunization rates in the United States are decent, experts reasoned.
"Part of it depends on how you are slicing and dicing this," said Dr. Robert Frenck, professor of pediatrics at Cincinnati Children's Hospital and a committee member of the American Academy of Pediatrics' committee on infectious diseases. "If you look at children going into kindergarten [four to six years old], our immunization rates are as high or higher than they've ever been."
"This is a little bit of a wake-up call -- not a huge one -- that you need to make sure to do the best you can to get children vaccines when they're supposed to get them," added Dr. Paul Offit, director of the Vaccine Education Center and chief of infectious diseases at the Children's Hospital of Philadelphia. He stressed that "kids may catch up [when they're older]."
Parents and kids face a complicated schedule of vaccinations in the first years of life. Some might even say it's a logistical nightmare. This study was based on doses kids received in 2003 and 2004, at which time a toddler up to 18 months old should have received about 14 shots related to several different vaccines. Today, there are even more shots recommended.
For 50 years, the success of the vaccination program has been measured by whether or not children received the required number of doses.
"[But] the official recommendations for vaccination include more than just number of doses," said Elizabeth Luman, lead author of the study and an epidemiologist at the CDC's National Center for Immunization and Respiratory Diseases in Atlanta. They also include specific age recommendations and often multiple doses at different time intervals.
For this study, researchers looked at vaccination histories for more than 17,500 U.S. children aged 19 months to 35 months.
An estimated 72 percent of children in this age group finished the standard vaccination series. That was 9 percentage points lower than if coverage was based on counting doses only, the researchers noted.
Nineteen percent of children were missing one or more doses of vaccines; 8 percent had received an "invalid" dose, meaning it was given while the child was too young or too close to the previous dose.
About 3 percent of the sample had their last hepatitis B vaccine too early (before six months). Some also received their measles vaccine while they were still protected by their mother's antibodies. Another 3 percent received serial doses of one vaccine too close together.
"If children receive vaccines too close together or too early, they're not as likely to be protected, and if you have a lot of that, then you're more likely to have disease outbreaks," Luman said.
One reason for lack of strict adherence to the vaccine schedule may be a fading consciousness among today's parents of what these immunizations are protecting children against. Frenck said he remembers seeing a childhood friend in an iron lung, the result of polio.
"It scared me to death," he said. "Kids these days, and probably most adults, don't even known what an iron lung is -- and that's because of immunization."
So far, smallpox has been completely eradicated from the planet thanks to immunizations, while great gains have been made with measles and polio.
"People just need to keep their vigilance up," Frenck said. "We need to continue to review shot records and to go over it with parents whenever they come in. Opportunities for vaccination are missed a lot of times when kids come in for one reason or another, and we don't look at the immunization record. We need to continue to try to immunize kids whenever we have the opportunity."
For more on vaccines and vaccine schedules, visit the CDC's Advisory Committee on Immunization Practices.