inference that distinguishes among these three scenarios. Thus, any conclusions drawn are based on the assumption that any one or more of these scenarios might be the “true” explanation. The committee's conclusions take into account the fact that these data do not support any one of these scenarios over the others.

  1. DPT administration might cause a serious acute neurologic illness and subsequent chronic nervous system dysfunction in children who otherwise might not have experienced either an acute neurologic illness or chronic nervous system dysfunction in the absence of DPT. If this were the sole explanation for the relation between DPT and chronic nervous system dysfunction, the committee would conclude that the relation is causal and that DPT increases the risk of chronic nervous system dysfunction in children.

  2. DPT might trigger (and thereby be an immediate or proximate cause —but nevertheless, still a cause) an acute neurologic illness and subsequent chronic nervous system dysfunction in children with underlying brain or metabolic abnormalities. These abnormalities might make the children susceptible to reacting adversely (with an acute neurologic illness) to stimuli (e.g., fever, infection, vaccines) that in children without such abnormalities might be well-tolerated. Thus, these children might have experienced chronic nervous system dysfunction even in the absence of DPT administration secondary to some other, non-DPT-related acute event. If this “triggering” by DPT of the acute event were the sole explanation for the relation between DPT and chronic nervous system dysfunction, the committee would conclude that the relation with the acute event is causal, but that DPT might not increase the overall or lifetime risk of chronic nervous system dysfunction in children, because the children who react to DPT might eventually have experienced some other type of acute illness that also could lead to chronic nervous system dysfunction.

  3. DPT might cause an acute neurologic illness in children with underlying brain or metabolic abnormalities that would themselves eventually have led to chronic nervous system dysfunction even in the absence of an acute neurologic illness. That is, the presence of underlying brain or metabolic abnormalities might predispose the child to react to DPT with an acute neurologic illness, but it is the underlying abnormality that is the cause of the chronic nervous system dysfunction, not the acute illness. DPT vaccination in this context would be a kind of “provocative challenge” unmasking the underlying abnormality. If this were the sole explanation for the relation between DPT and chronic nervous system dysfunction, the committee would conclude that the relation is not causal and that DPT administration does not increase the overall risk for chronic nervous system dysfunction.



The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement