Immunization to protect infants and children from vaccine-preventable diseases is one of the greatest achievements of public health. Immunization is not without risks, however. It is well established, for example, that the oral polio vaccine can on rare occasion cause paralytic polio.

The Immunization Safety Review Committee was established by the Institute of Medicine (IOM) to evaluate the available evidence on a series of immunization safety concerns. The committee is charged with examining three immunization safety hypotheses each year during the three-year study period (2001– 2003). While all of the committee members share the view that immunization is generally beneficial, none of them has a vested interest in the specific immunization safety issues that come before the group. In this report, which is the fourth in the series, the committee examines the hypothesis that the hepatitis B vaccine increases the risk for demyelinating disorders of the central or peripheral nervous systems, including multiple sclerosis (MS) and Guillain-Barré syndrome (GBS). The conclusions and recommendations of the committee’s first three reports—Immunization Safety Review: Measles-Mumps-Rubella Vaccine and Autism (IOM, 2001a), Immunization Safety Review: Thimerosal-Containing Vaccines and Neurodevelopmental Disorders (IOM, 2001b), and Immunization Safety Review: Multiple Immunizations and Immune Dysfunction (IOM, 2002)— are summarized in Appendix A.

For each hypothesis to be examined, the committee assesses both the scientific evidence and the significance of the issue for society.

The scientific assessment has two components: an examination of the epidemiological and clinical evidence regarding a possible causal relationship between the immunization and the adverse event; and an examination of biological theory and experimental evidence (from studies in humans, animals, or in vitro systems) regarding mechanisms that might be relevant to the hypothesis.

The significance assessment addresses such considerations as the burden of the health risks associated with the vaccine-preventable disease and with the adverse event in question, as well as the level of public concern about the safety issue.

The Immunization Safety Review Committee has adopted the framework for assessing causality developed by its predecessors (convened by the IOM in 1991 and 1994 under congressional mandate of P.L. 99–660) to address questions of immunization safety. The categories of causal conclusions used by the committee are as follows:

  1. No evidence

  2. Evidence is inadequate to accept or reject a causal relationship

  3. Evidence favors rejection of a causal relationship

  4. Evidence favors acceptance of a causal relationship

  5. Evidence establishes a causal relationship.

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