1 in 4 U.S. Toddlers Improperly Vaccinated

TUESDAY, April 29 (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 theAmerican 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.