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Adverse Events Associated with Childhood Vaccines: Evidence Bearing on Causality
There are reports of GBS following vaccination, but it is difficult to determine whether the frequency is greater than expected. There is some biologic plausibility for this association in terms of the occurrence of GBS following hepatitis B infection, the occurrence of demyelinating disease following vaccination in general (see Chapter 3), and the fact that cases have been reported in various countries and with various versions of both plasma-derived and recombinant vaccines. The episodes of GBS that occurred outside the United States are too rare to make any calculation of the incidence of GBS, and no value for the denominator is available. For New Zealand, a calculation of the incidence of GBS was made by using data from Olmsted County, Minnesota, for comparison. This seems inappropriate for geographic and demographic reasons. For the postmarketing surveillance data (Shaw et al., 1988), the authors assumed that the denominator was at least 850,000, which gives a crude rate of slightly greater than 1 case per 100,000 people receiving the vaccine. Shaw and colleagues examined the incidence rate of GBS in hepatitis B vaccine recipients in more depth using background rates from both Olmsted County and a national Centers for Disease Control study, and they also adjusted the data for age and sex. Some of the analyses of Shaw and colleagues, primarily those comparisons using the CDC data, reported a significant increase in the risk of GBS. However, the committee thought that the evidence was not conclusive for many of the same reasons Shaw and colleagues discussed in their report.
The evidence is inadequate to accept or reject a causal relation between hepatitis B vaccine and GBS.
OTHER DEMYELINATING DISEASES
Three central nervous system demyelinating diseases have been reported to occur following hepatitis B vaccination: a chronic demyelinating disease, multiple sclerosis, and two focal demyelinating lesions, optic neuritis and transverse myelitis. In patients with multiple sclerosis, demyelinating lesions occur in multiple locations and at different times. Transverse myelitis is characterized by the acute onset of signs of spinal cord disease, usually involving the descending motor tracts and the ascending sensory fibers, suggesting a lesion at one level of the spinal cord. On several occasions, it has been described as occurring after vaccination. The annual