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Adverse Events Associated with Childhood Vaccines: Evidence Bearing on Causality
Proposed Electrodiagnostic Criteria for Demyelination of Peripheral Nerve
These criteria concern nerve conduction studies (including proximal nerve segments) in which the predominant process is demyelination. Must have three of the following features:
Reduction in conduction velocity in two or more motor nerves.
<80 percent of the lower limit of normal (LLN) if the amplitude is >80 percent of LLN.
<70 percent of LLN if the amplitude is <80 percent of LLN.
Conduction block or abnormal temporal dispersion in one or more motor nerves: either the peroneal nerve between the ankle and below the fibular head, median nerve between the wrist and elbow, or the ulnar nerve between the wrist and below the elbow.
Criteria for partial conduction block:
>15 percent change in duration between proximal and distal sites and >20 percent drop in the negative-peak area or peak-to-peak amplitude between the proximal and distal sites.
Prolonged distal latencies in two or more nerves.
>125 percent of the upper limit of normal (ULN) if the amplitude is >80 percent of LLN.
>150 percent of ULN if the amplitude is <80 percent of LLN.
Absent F-waves or prolonged minimum F-wave latencies (10-15 trials) in two or more motor nerves.
>120 percent of ULN if the amplitude is >80 percent of LLN.
>150 percent of ULN if the amplitude is <80 percent of LLN.
Source: Adapted from Asbury and Cornblath (1990).
Safranek et al., 1991; Schonberger et al., 1979), the risk of developing GBS in the 6 weeks following vaccination was some six- to eightfold greater than that for those who were not vaccinated, even though the overall incidence was only about 1 per 100,000 vaccinees. What it was about the swine flu vaccine that led to GBS on rare occasions has never been discovered; nevertheless, the capacity of that particular vaccine to trigger excess cases of GBS is thoroughly documented. In addition, the clinical features of GBS following swine flu vaccination resembled in all respects those
