Controlled Observational Studies

There have been no controlled observational studies investigating an association between Hib vaccines and GBS.

Controlled Clinical Trials

GBS has not been reported in any of the controlled clinical trials of plain PRP or PRP conjugate vaccines that have been performed (Barkin et al., 1987; Black et al., 1991b; Campbell et al., 1990; Claesson et al., 1988, 1989; Clements et al., 1990; Dashefsky et al., 1990; Decker et al., 1992; Eskola et al., 1987, 1990a,b; Ferreccio et al., 1991; Frayha et al., 1991; Granoff and Osterholm, 1987; Greenberg et al., 1987; Hendley et al., 1987; Kayhty et al., 1988, 1989; Kovel et al., 1992; Lenoir et al., 1987; Lepow et al., 1984a,b, 1985, 1986, 1987; Peltola et al., 1977; Santosham et al., 1992; Watemberg et al., 1991).

Causality Argument

There are no animal models of GBS following immunization for Hib; however, Chapter 3 presents evidence that GBS is biologically plausible as a consequence of vaccines in general. Data bearing on causality are limited to case reports. Seven cases labeled as GBS were reported to occur following immunization with three different Hib conjugate vaccines over a period when an estimated several million doses of Hib conjugate vaccines were distributed. Five of these cases fit the criteria for possible vaccine-related GBS discussed in Chapter 3. Hib conjugate vaccine administration was the only potential predisposing factor cited for the development of GBS in three of the five children who fit the case definition of GBS following immunization for Hib. Gervaix and colleagues (1993) speculated that the anti-PRP IgM antibodies detected in the plasma of the patient they described might have cross-reacted with glycoproteins of peripheral nerve myelin, leading to GBS. Two of the five children who developed GBS following immunization with Hib vaccine had possible predisposing factors (infections, OPV immunization) other than Hib immunization.

Conclusion

The evidence is inadequate to accept or reject a causal relation between Hib vaccines and GBS.



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