in other surveillance programs. With the increasing importance of population-based approaches to health system planning and evaluation, immunization registries offer one of the most useful instruments for assessing the population-specific effectiveness of health and medical care programs.

Finding 4–8. The registries of most states have not achieved a level of performance that allows them to serve as effective sentinels for gaps in coverage. A number of barriers need to be addressed if registries are to be fully implemented. Broad variability, the lack of consistent technical standards, problems with access to and the operational capability of software to support registry operations, and the need to respond to the requirements of multiple jurisdictions constitute major challenges that must be resolved to improve registry performance. Making registries fully operational will entail considerable costs, as well as efforts to resolve key concerns about privacy, liability, and confidentiality.

Finding 4–9. Data gaps and unreliable measures can lead to under-estimation of coverage levels and risk of disease for vulnerable populations. These uncertainties could eventually lead to blind spots within the national immunization system that would create pressure points in policy and practice and erode the quality and integrity of the enterprise. The experience with measles outbreaks in 1989–1991 and more recent disease reports suggest that during periods of complacency, low levels of immunization coverage among vulnerable groups may remain undetected and unaddressed, and can erupt into infectious disease outbreaks (NVAC, 1991).

Monitoring Vaccine Safety

As a biological product, vaccines may cause unintended side effects, some of which can be serious. Concerns about quality, safety, and reliability can be expected to grow as use of vaccines expands, particularly as the threat of infectious disease diminishes and as knowledge of the possible long-term health consequences of vaccine use increases. The potential for adverse events argues for the need to sustain both reliable monitoring systems and sources of expertise that can investigate anecdotal and clinical reports. The ability to distinguish between causal relationships and coincidence should adverse events occur requires an evidentiary base, as well as risk assessment judgments that can guide health care and public policy decisions during periods of uncertainty. Extensive media coverage of claims about possible adverse events associated with vaccine use before research information is available to guide health professionals, policy

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