The 2002–2004 period was a challenging time in Colorado with regard to immunizations. Given the circumstances, TCHD chose to explore barriers to immunization among high-risk groups, such as the WIC population. In TCHD's study, baseline UTD rates for its WIC population were substantially below the national, Healthy People 2010
target of 90%, confirming the undervaccination of this group.12
Moreover, in the TCHD study, as in numerous other studies, A/R interventions improved these UTD rates.6–10
In this study, numerous vaccine types were found to be missing among non-UTD children. However, an important finding for TCHD was the poor DTaP coverage among its WIC population, along with the discrepancies between mother-reported and actual UTD status with regard to DTaP. This discrepancy may have occurred due to confusion related to the DTaP vaccine shortage. This finding illustrated the need for local health departments to conduct their own assessments on vaccine coverage within their WIC populations, rather than simply rely on national data, as missing vaccines may vary based on location or unique regional circumstances.
This finding also highlights the need for TCHD to target DTaP specifically in educational messages for WIC mothers, particularly now that the shortage has ended, as it may add further confusion about DTaP dose requirements. With a 116% rise in reported pertussis cases in the TCHD jurisdiction in 2004, it is important to educate WIC mothers about pertussis as well, thereby further emphasizing the importance of vaccination.
The findings regarding DTaP may also affect future A/R strategies employed at TCHD WIC clinics. Research has suggested assessing DTaP coverage alone in WIC clinics as a proxy for assessing overall UTD rates, thereby reducing workload.13,14
While this strategy may be valuable in some locales, it may be less useful in the TCHD setting. In Clinic D, for example, while DTaP was the most commonly missing vaccine among non-UTD children (68%), counting only these children as non-UTD would have missed 32% of non-UTD children. This strategy would have artificially inflated the baseline UTD rate in Clinic D from 68% to 78%.
Assessing DTaP alone in TCHD WIC clinics may thus be less effective in identifying non-UTD children. In some WIC settings, missing non-UTD children may be less important as compared to workload. However, given the immunization-related challenges in Colorado, TCHD's goal was to identify as many non-UTD children as possible, making this work-reducing strategy less viable. Local public health agencies should consider assessing their own goals, along with DTaP coverage in their own WIC populations, prior to applying this method.
This study also helped identify immunization-related barriers specific to the TCHD WIC population. Other studies have shown higher risks of undervaccination based on factors such as maternal race, education, number of children, and insurance status.5,15,16
In TCHD's WIC population, it appears that lack of insurance is an important risk factor. These clients represent a vulnerable subpopulation that should be targeted in future interventions.
This study had several limitations. Differences in sampling methods at one of the clinics prevented merging of the data from all four sites. Merging would have given greater power to the analysis, and may have elucidated other significant associations. Another limitation was that no follow-up assessment or review of missing vaccines was done in Clinic A, which limited our analysis of that site.
As a result of this study, several actions have been taken. TCHD is now conducting A/R interventions at all of its WIC clinics. Moreover, TCHD's WIC immunization programs are increasing educational efforts regarding DTaP as well as pertussis. Efforts are also being made to identify and educate uninsured WIC mothers about low-cost or free vaccination programs available at TCHD and throughout the community.