Chapter 2) or noncases, based on responses to the questionnaire. As part of an extensive laboratory evaluation, the authors tested serum samples for antibodies to type A botulinum toxin and the anthrax protective antigen or lethal factor (to screen for exposure to the vaccines or toxins). The study found that 10 of the 158 individuals had antibodies to the botulinum toxin and 14 to the anthrax protective antigen; however there were no differences in reactivity rates between cases and noncases.

The clinical evaluation part of this study examined a small sample of veterans from one unit deployed to the Gulf War theater and did not rely on a random sample. The issues of bias and lack of power must be considered in interpreting the results of this study.

Conclusions on Human Studies

Certain multiple vaccination regimens can lead to suboptimal antibody responses, but there is little evidence, largely because of a lack of active monitoring, of other adverse clinical or laboratory consequences beyond the transient local and systemic effects seen frequently with any vaccination.

No long-term, identifiable clinical sequelae attributable to intense long-term immunization occurred in the Fort Detrick cohort. There was some evidence of a chronic inflammatory response, but these changes cannot necessarily be attributed to the vaccinations, since the workers studied were occupationally exposed to a number of virulent microbes. This series of longitudinal clinical studies also had several shortcomings. However, the Fort Detrick study is valuable because careful monitoring did not disclose any evidence of serious unexplained illness in a cohort that received a series of intense vaccination protocols over many years.

The U.K. Gulf War studies provide some limited evidence of an association between multiple vaccinations and long-term multisymptom outcomes, particularly for vaccinations given during deployment (Unwin et al., 1999; Hotopf et al., 2000). There are some limitations and confounding factors in these studies, and further research is needed.

The committee concludes that there is inadequate/insufficient evidence to determine whether an association does or does not exist between multiple vaccinations and long-term adverse health effects.

This finding means that the evidence reviewed by the committee is of insufficient quality, consistency, or statistical power to permit a conclusion regarding the presence or absence of an association between multiple vaccinations and health outcomes in humans.



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