Decker et al., 1992; Granoff et al., 1988; Hetherington and Lepow, 1992; Holmes et al., 1991; Insel and Anderson, 1986; Parke et al., 1991; Schlesinger and Granoff, 1992; Shackelford and Granoff, 1988). These differences produce subtle functional differences in vitro, but the implications for protective activity in vivo are unknown (Amir et al., 1990a,b).

Individuals who produce protective levels of antibody to Hib vaccines generally do so within 1 month of immunization (Kayhty et al., 1989; Peltola et al., 1977). Good immune responses to the conjugate vaccines have been demonstrated as soon as 1 week after immunization in older children and adults (Daum et al., 1989; Marchant et al., 1989).

Unlike plain PRP vaccines, PRP conjugate vaccines stimulate memory B cells capable of generating booster responses to immunization with either plain PRP or PRP conjugate vaccines and, thus, presumably, to the intact Hib organism (Weinberg et al., 1987). PRP conjugate vaccines reduce the Hib oropharyngeal carrier state (Barbour, 1992; Mohle-Boetani, 1992; Murphy, 1991; Takala et al., 1991).


Clinical Description

Myelitis is inflammation of the spinal cord. Transverse myelitis is myelitis in which the inflammatory process principally involves one or more spinal cord segments, showing the manifestations of a transverse cord lesion that usually develops acutely. Initially, many cases of transverse myelitis are not complete. Early symptoms in some patients include sphincter paralysis associated with a total or partial loss of sensation below the level of the lesion. As the acute spinal shock resolves, the paraplegia becomes spastic. Acute multiple sclerosis and postinfective myelitis are among the commonest causes of this syndrome. The annual incidence of transverse myelitis in Rochester, Minnesota, from 1970 to 1980 was 0.83 per 100,000 people (Beghi et al., 1982).

History of Suspected Association

The history of a suspected association between Hib vaccines and transverse myelitis is based solely on three case reports in the Vaccine Adverse Event Reporting System (VAERS). There are no reports in the literature of an association between Hib vaccines and transverse myelitis.

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