Role of Immunization Registries in Improving Coverage Levels. Immunization registries serve multiple purposes beyond the surveillance and assessment of current coverage rates (DeFriese et al., 1999). They can facilitate service delivery, consolidate scattered records, and simplify the assessment of need for vaccine for both private and public providers. As long as significant numbers of at-risk groups are enrolled, registries can also be used to identify pockets of need in areas where immunization coverage lags behind the current high national and/or state levels. If used appropriately, fully operational registries can be an efficient means of identifying children who require intensive services and may stimulate service responses to ensure their full immunization.

In addition to improving immunization coverage for the currently recommended immunization schedule, registries can be used to monitor and ensure the full implementation of newly recommended vaccines and vaccine schedules. Just as a series completion rate for children in the registry catchment area can be assessed, uptake of specific antigens, including those newly introduced, can be monitored and changes made in implementation strategies on the basis of populations identified as being in need. The current immunization schedule is sufficiently complex to benefit from computerized monitoring, and, as noted earlier, greater complexity is anticipated in the future.

Anecdotal reports (Fairbrother et al., 1997) indicate that immunization monitoring can also improve the identification of children who require other preventive care services (such as lead screening). It is conceivable that investments in immunization registries could benefit these programs, although the scale of this potential impact is not known. The costs and benefits of immunization registries for adult populations (particularly those over age 65) are similarly uncertain.

Barriers to Registry Development and Implementation. Barriers to registry development and implementation fall into four categories: (1) technical and operational issues, (2) privacy and confidentiality, (3) provider participation, and (4) resource requirements (NVAC, 1999b; Linkins and Feikema, 1998; Kilbourne, 1998).

Difficulties have been experienced in sharing information among community-based registries because of variations in the architecture of computer systems, including different software, hardware, data entry mechanisms, and networking resources (NVAC, 1999b). Differences also exist in the methods used to receive or send registry data and in linkages to other computer systems. CDC has encouraged its state and local grantees to endorse standard algorithms to facilitate the transfer of information between systems (NVAC, 1999b; Wood et al., 1999). Duplicate records,