More than one in four children are not in compliance with official vaccination recommendations because of missed doses of vaccines or vaccine lapses -- meaning that the vaccines were given at the wrong age or at the wrong intervals -- researchers at the CDC found.
The CDC researchers studied vaccine coverage histories for 17,563 2-year-old children in 2005 based on federal guidelines that specify vaccines for administration, dosages, age ranges and the intervals between doses.
Traditionally, the government has measured immunization noncompliance by tallying up only missed doses of a vaccine. In this new research, the CDC recalculated immunization compliance to include vaccine lapses in addition to missed doses. Based on these new criteria, the CDC found that immunization compliance was actually 9 percentage points lower than previous estimates, dropping the compliance rate from 81 percent to 72 percent.
"It's really important that parents understand how important it is to get their kids vaccinated on time and within the recommended guidelines," lead study investigator Elizabeth Luman of the National Center for Immunization and Respiratory Diseases said. "It's important for both the health of the child and the health of the public."
Luman added that although the current measles outbreak in California and Arizona is due mostly to people who haven't been vaccinated at all, those who haven't complied with the appropriate timing and age recommendations of vaccine doses may also contract and spread the diseases.
"If you have vaccinations too early or too close together, they're less effective," Luman explained. "And on a population basis, that really increases your risk of outbreaks."
Some doctors believe that vaccine lapses may have played a role in the recent outbreaks of various preventable diseases in the United States, such as measles and mumps.
"Vaccination at the wrong age or the wrong interval is not a major danger from the perspective of eventual immunity induced by the vaccine," said Dr. Michael Pichichero, professor of microbiology and immunology at the University of Rochester Medical Center.
"The public health issue is the lack of full protection from a disease until the vaccination series is completed. ? The recent various outbreaks of measles, mumps and other vaccine-preventable diseases brings attention to the risks parents need to know they are accepting."
According to infectious disease experts, the most obvious explanation for noncompliance is confusion over which vaccine a child needs, how many doses and in what intervals.
With about 10 recommended vaccinations for children around age 2, almost all of which require two or more doses within a specified time period, Luman believes that some parents might find it difficult to keep it all sorted out.
"It's a complicated schedule ? and there are also a lot of vaccines and figuring out when to time them can be a bit complicated," Luman said.
Another possible factor may be vaccine shortages.
"The U.S. vaccine industry is in chaos due to [a] lack of huge available profits in this sector. ? There are constant shortages of one vaccine or another," said Dr. David Freedman, professor of medicine and epidemiology at the University of Alabama at Birmingham.
"In many cases when there is a shortage, physicians can't get any, stop giving it and are not rapidly informed when it is available again. In some cases shortages or nonavailability can last a year or more."
Although Luman said a lack of certain vaccines might have contributed to noncompliance, she believes it had more to do with the specific practices of parents and health-care providers.
Luman also identified another possible reason why so many children were out of compliance with the age and timing recommendations for vaccines: the lack of a primary-care physician.
"The physician may not have known when the exact timing of the previous dose was, especially if the child goes to more than one physician," Luman explained. "Maybe the physician didn't have all [the] information to give an appropriately dated vaccine."
Possibly as a result, the researchers found that many parents vaccinated their child too early to meet the recommended age requirements for a specific vaccine dose, thereby invalidating the vaccine's protection altogether.
Registries May Help
Amy Pisani, the executive director of Every Child by Two, an advocacy group for raising awareness of timely immunizations for all children, echoed Luman's concerns regarding the possible reasons for low compliance rates.
"It is confusing and there [are] so many vaccinations you need now by age 2 that parents have trouble keeping track of them," Pisani said. "We also have a large migrant population, a lot of dual working families. ? All these things rolled up into one make it very difficult to keep track of what vaccination each child needs and when."
Pisani believes the answer to this problem lies in the use of immunization registries, a comprehensive resource for storing all patients' immunization histories so that one patient's records aren't lost when they move from one doctor to another.
Just as veterinarians will send out cards to their patients to remind them which immunizations their animal is not up to date on and when their pet is due back for more vaccinations, these immunization information systems allow doctors to easily check up on patient's vaccination records and send out reminders to those who due for follow-up vaccine doses.
"The up-to-date status goes way up in populations that use the registries because it's so much easier to track them," Pisani explained. "Instead of an entire education campaign to raise awareness of the importance of getting all of your immunizations, doctors can just look up the patients who are not up-to-date and call them up to remind them."