The committee organized these conclusions into five categories. Because some confusion has arisen over the meaning of the category descriptions used by the Committee to Review the Adverse Consequences of Pertussis and Rubella Vaccines, despite extensive explanations in both the footnotes and the text, the Vaccine Safety Committee adopted some minor modifications in wording intended to help in the interpretation of the present report. To facilitate reading by those familiar with the report of the previous committee, the present committee maintained both the number of categories (five) and the order of those categories but modified the wording in an attempt to clarify its meaning. However, the Vaccine Safety Committee (which has some overlap in committee membership and staff with the earlier committee) believes that the categories represent the same concepts intended by the predecessor committee. The categories are:

  1. No evidence bearing on a causal relation.

  2. The evidence is inadequate to accept or reject a causal relation.

  3. The evidence favors rejection of a causal relation.

  4. The evidence favors acceptance of a causal relation.

  5. The evidence establishes a causal relation.

Chapter 2 contains a discussion of the criteria used by the committee for each determination of the final weight of evidence.

The evidence favors rejection of, favors acceptance of, or establishes a causal relation between a vaccine and an adverse event in approximately one-third of the relations studied. For the other relations the evidence was inadequate to accept or reject a causal relation or there was no evidence bearing on the relation. It is important to note that the use of the term inadequate does not necessarily imply that the data were scarce. In some cases the committee identified an abundance of data. However, as a whole, it did not favor either acceptance or rejection of a causal relation. In the lists below, the superscript letters refer to the appropriate notes in Table 1-2. The notes in Tables 1-1 and 1-2 are integral to interpretation of the findings. The committee reached the following conclusions regarding causality.

The evidence favors rejection of a causal relation between:

  • diphtheria and tetanus toxoids and encephalopathy,e infantile spasms,f and death from sudden infant death syndrome (SIDS),f,g and

  • conjugate Hib vaccines and early-onset Hib disease.

The evidence favors acceptance of a causal relation between:

  • diphtheria and tetanus toxoids and Guillain-Barré syndromeh and brachial neuritis,h

  • measles vaccine and anaphylaxis,d

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