Learning Objectives for this Presentation:
By the end of this presentation participants will be able to describe extraimmunizations in US children as documented by immunization information systems (IIS).

Background:
Little is known about the extent of extraimmunization among US children. We utilized data from the 6 IIS sentinel projects to assess extraimmunization in children born during 1999 to 2003.

Objectives:
To determine the extent of extraimmunization in children and identify associated risk factors.

Methods:
Extraimmunization was defined as having more than the recommended number of doses of any vaccine by 18 months of age (excluding varicella and PCV): 4 DTP/DTap, 3 polio, 1 MMR, 4 Hib, and 4 Hepatitis B. The number of children extraimmunized at 35 months of age was calculated by sentinel project and birth cohort year (1999-2003) separately. Chi-square tests were performed to test for significant associations between demographic factors and extraimmunization.

Results:
For all vaccines considered and all cohorts, the percent extraimmunized (averaged over the 6 projects) was <3%, except for polio (≤6%). The percent of children extraimmunized with ≥1 dose of vaccine (averaged over the 6 projects) decreased from 10.5% in 1999 to 7.9% in 2003. In general, children with more than 1 provider and who were seen at a mixture of public and private sector provider sites were significantly more likely to be extraimmunized (P<0.01).

Conclusions:
These data indicate that the percent of extraimmunization for each of the 5 vaccines examined was low. The decline of polio vaccine extraimmunization may reflect decreasing confusion with time since discontinuing oral polio vaccine in 2000. Use of IIS can help to monitor extraimmunizations, and may also help to minimize extraimmunizations, particularly among children with multiple immunization providers.