TUESDAY, March 8 (HealthDay News) -- More than one in three U.S. children are "under-vaccinated" for more than six months during the first two years of life, a new study finds.
"We were really surprised to find that such a large proportion of kids are delayed for such a large portion of their first two years," said study author Elizabeth Luman, an epidemiologist with the National Immunization Program in Atlanta.
The delays put children at risk for a variety of vaccine-preventable diseases such as measles, mumps and chicken pox, the researchers said.
"They will be less protected against various diseases," confirmed David Neumann, executive director of the National Partnership for Immunization.
Children in the United States are supposed to receive about 15 to 20 vaccinations during the first 24 months of life, all of them delivered on a complicated schedule involving specific age recommendations and often multiple doses at different time intervals.
While almost three-quarters (73 percent) of U.S. children receive all the recommended vaccinations, only 9 percent are receiving all their vaccinations at the recommended times, the researchers found.
"We're doing a really good job of making sure kids are vaccinated, especially by school age. But, if you look at it a little more closely, they're not getting all the vaccinations when they're supposed to," Luman said.
The study findings appear in the March 9 issue of the Journal of the American Medical Association.
For the study, Luman and her colleagues wanted to measure the delays for the 91 percent of children who were not following exact protocol. The researchers looked at data on 14,810 children aged 24 months to 35 months that had been collected as part of the 2003 National Immunization Survey.
Overall, children were under-vaccinated -- meaning they were late in getting a vaccine or hadn't received the full dose -- an average of 126 days for all vaccines during the first 24 months of life.
About one-third (34 percent) were under-vaccinated for less than one month, 29 percent for one to six months and 37 percent for more than six months.
About one-quarter of children had delays in receiving four or more of six important vaccines, including the measles-mumps-rubella vaccine. Approximately one in five (21 percent) children were severely delayed, meaning they had delays of more than six months, and were late for four of the six vaccines, the study found.
These "severely delayed" children were more likely to have a mother who was unmarried or didn't have a college degree, to belong to a household with two or more children, to be non-Hispanic black, to have two or more vaccination providers or to have had a public vaccination provider.
"It's really important that kids get vaccinated on time, especially during the first two years because that's when they are at highest risk for many of the vaccine-preventable diseases," Luman said. "When they aren't vaccinated on time, they are left susceptible to disease until they're vaccinated. The question is how bad is it."
The answer depends on how late a child gets vaccinated, and whether he or she has been exposed to the disease.
"If they happen to be a month late and were exposed to the disease then, for them, a month was too long," Luman said. "Clearly, late is better than never and a little bit late is better than a lot late. But if we can keep them from falling behind, that's the best."
Health-care providers need to work to identify children who are at risk and encourage their parents to bring them in, Luman said. Providers can also offer reminders and longer office hours for parents who work.
"Timely vaccination is one of the most important things a parent can do to protect the health of their children," Luman said. "It's easy in theory and difficult in practice."
Neumann said: "One of the challenges we face every day is a lot of young parents who have never seen measles or have never seen chicken pox or what have you, and convincing them that it's worth the time to get the child into the doctor's office or public health clinic to be immunized in a timely manner. We have to remind them that even though they haven't seen these diseases they are very real and can be deadly."
Get more information on the vaccination schedule at the National Immunization Program.