Neither of these interpretations is correct. “Inadequate to accept or reject” means just that—inadequate. If there is evidence in either direction that is suggestive but not sufficiently strong about the causal relationship, it will be reflected in the weight-of-evidence assessments of the epidemiologic or the mechanistic data. However suggestive those assessments might be, in the end the committee concluded that the evidence was inadequate to accept or reject a causal association.

The committee does want to emphasize many of the adverse events examined are exceedingly rare in the population overall, and in most instances any particular adverse event, be it arthritis, meningitis, or any of the other vaccine–adverse events that the committee considered, are not preceded by immunization. The committee chose cautious and scientific language for our conclusions, because, especially with rare events, it is not possible to prove a negative (i.e., the vaccine did not and cannot cause the event). The committee cannot say that in a certain person at a certain time, some event cannot happen; there is much about biology that is not known.

The committee tried to apply consistent standards when reviewing individual articles and when assessing the bodies of evidence. Some of the conclusions were easy to reach; the evidence was clear and consistent or, in the other extreme, completely absent. Some conclusions required substantial discussion and debate. Inevitably, there are elements of expert clinical and scientific judgment involved.

The committee used the best evidence available at the time. The committee hopes that the report is sufficiently transparent such that when new information emerges from either the clinic or the laboratory, others will be able to assess the importance of that new information within the approach and set of conclusions set forth in this report.

The committee hopes this summary of the thinking of the committee is helpful to the reader.


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Chapman, R. S., K. W. Cross, and D. M. Fleming. 2003. The incidence of shingles and its implications for vaccination policy. Vaccine 21(19-20):2541-2547.

Farrington, P., S. Pugh, A. Colville, A. Flower, J. Nash, P. Morgan-Capner, M. Rush, and E. Miller. 1995. A new method for active surveillance of adverse events from diphtheria/ tetanus/pertussis and measles/mumps/rubella vaccines. Lancet 345(8949):567-569.

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