In the United States, the Department of Health and Human Services, through the Food and Drug Administration (FDA) and the Centers for Disease Control and Prevention (CDC), has responsibility for ensuring vaccine safety. Within CDC, the National Immunization Program (NIP) is responsible for assisting health departments with immunization programs, supporting the establishment of vaccine supply contracts, administering research and operational programs for the prevention and control of vaccine-preventable diseases, and monitoring the safety and efficacy of vaccines (CDC, 2001). The NIP, in conjunction with its colleagues at FDA, uses a variety of means to continually evaluate vaccine safety, including signal detection through reports from the Vaccine Adverse Event Reporting System (VAERS), ad hoc epidemiologic studies, state and community immunization registries, and laboratory surveillance. Another resource that has been used since 1991 to evaluate vaccine safety is the Vaccine Safety Datalink (VSD).

The VSD is a large linked database that was developed in 1991 through the collaborative efforts of CDC and several private managed care organizations (MCOs) (Chen et al., 1997). The VSD currently includes data from administrative records for more than 7 million members of eight MCOs (Davis, 2004). In the VSD, vaccination records, patient characteristics, and health outcomes are linked; this allows the VSD to serve as a unique and potentially powerful resource for the ongoing evaluation of vaccine safety (Davis, 2004). With its longitudinal data on reasonably well-defined cohorts, the VSD differs from VAERS, a passive surveillance system that depends on voluntary reporting. Both data sources have strengths and limitations, but they complement one another.

The opportunities offered by the VSD for thorough investigations of vaccine safety concerns and well-designed, planned, retrospective vaccine studies have led to heightened interest in the results of VSD studies and sometimes in the VSD data themselves. A few researchers interested in particular vaccine safety hypotheses also have shown interest in accessing and analyzing VSD data. The interest in the VSD shown by researchers, advocacy groups, members of Congress, and others has brought increasing attention to its use, its limitations, and the implications of studies that were conducted through the analysis of its data.


The Institute of Medicine (IOM) Committee on the Review of the National Immunization Program’s Research Procedures and Data Sharing Program was convened at the request of the NIP to offer advice on two

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