Behind the Numbers: State Variation in Childhood Immunization Coverage Rates

Background: Achieving and maintaining high childhood immunization rates is an ongoing public health challenge. Although the federal government plays a significant role in the financing of vaccines and state immunization program operations, the primary responsibility to assure adequate immunization levels falls to the states.

Objectives: In order to better understand state variation in childhood immunization rates, this analysis aimed to: 1) identify population and provider-based characteristics associated with under-immunization among preschool age children, 2) identify state policies and practices that may influence childhood immunization rates, and 3) test for differences in these characteristics, policies, and practices in states with high and low coverage rates.

Methods: States were divided into quartiles based on their childhood immunization coverage rate for the 4:3:1:3:3:1 vaccine series in the 2005, 2006, and 2007 National Immunization Survey. First quartile states were compared to fourth quartile states on a number of factors for each of the survey years using the Wilcoxon Rank Sum Test and Fisher’s Exact Test.

Results: Differences between high and low coverage states were detected. Fourth quartile (high coverage) states had higher proportions of children with private, employer-based insurance and births to mothers with at least four years of college and lower proportions of completely unvaccinated children and children living in low-income households. High coverage states were also associated with having insurance benefit mandates for immunization and requiring all vaccines for childcare. Finally, high coverage states served a greater proportion of their WIC participants at WIC clinic sites with immunization activities.

Conclusions: The findings were consistent with published research on determinants of immunization. Recommendations for states interested in achieving and maintaining high childhood immunization coverage rates were proposed. Multivariate analysis is needed to determine the extent of the impact of various measures on state coverage rates and potential interactions among measures tested.