Learning Objectives for this Presentation:
By the end of the presentation participants will be able to understand limitations of using Immunization Information Systems (IIS) to compare vaccination coverage between states.

Background:
IIS are potentially useful for supplementing missing provider data in the NIS. To evaluate this, the NIS conducted experiments in four areas with well-established IIS in 2002 and another four areas in 2004.

Objectives:
To compare quality and completeness of the vaccine-specific dose information collected from the IIS and providers in the NIS.

Methods:
Household respondents for the NIS-sampled children (aged 19-35 months) were requested to give consent to contact providers and registries to obtain vaccination histories. Among children with consent, we estimated coverage rates for the 4:3:1:3 vaccine series based on child's up-to-date status from: only IIS data; only provider data; and combined IIS and provider data.

Results:
Household respondents who gave consent to contact providers, 98% gave permission to contact registries in eight sites. Among children with consent, 505 (79%) had vaccination data from either IIS or providers in 2002 and 620 (96%) had data in 2004. In 2002, IIS-based 4:3:1:3 coverage rates were lower than the provider-based rates by -9.6, -13.4, -15.2, and -34.3 percentage points. In 2004, 4:3:1:3 estimates were -2.3, -8.9, -11.1 percentage points lower in three sites and +2.3 percentage points higher in one site. Vaccination coverage rates based on the combined IIS and provider data were higher than the estimates based on data from either source alone in all eight sites.

Conclusions:
Vaccination coverage rates were under-estimated using the IIS data alone in seven of the eight sites. Although IIS data can supplement NIS provider data, completeness of IIS data varied across sites. Until completeness of vaccination data improves to equivalent levels across all IIS, NIS will continue using provider-reported histories to compare state level vaccination coverage in the U.S.