following other antecedent events or no antecedent events. Monitoring for GBS following the administration of other influenza vaccines in the years subsequent to the 1976-1977 swine flu vaccine incident did not disclose any excess cases of GBS (Hurwitz et al., 1981; Kaplan et al., 1983; Roscelli et al., 1991).

It has been known for decades that GBS occurs following the administration of another vaccine, namely, rabies vaccine produced from the nervous tissue of an infected animal (Table 3-1). Because they are inexpensive, these vaccines are still made and used in certain parts of the world, including Asia and South America. Vaccine made from mature sheep or goat brain and then inactivated with phenol (Semple vaccine) causes encephalomyelitis as its main neurologic adverse event, and the reported incidence of such events is from I per 300 to I per 3,000 vaccinees (Hemachudha et al., 1987b, 1988). A small proportion, perhaps 15 percent, of Semple vaccinees who develop a neuroparalytic adverse event have characteristic GBS. Of interest, these patients develop high levels of antibody to myelin basic protein, a central myelin constituent in serum and cerebrospinal fluid (Hemachudha et al., 1987a, 1988). In contrast, rabies vaccine produced from infected suckling mouse brain induces, on occasion (approximately 1 in 7,500 vaccinees), a GBS-like syndrome (Lopez Adaros and Held, 1971). The clinical features tend to be unusually severe (Cabrera et al., 1987). These individuals rarely develop antibody titers to myelin basic protein (Hemachudha et al., 1988), which is consistent with the fact that the suckling mouse brain is unmyelinated. It is not clear what the basis for GBS might be following the administration of either Semple rabies vaccine or suckling mouse brain rabies vaccine, but most authorities believe that the neuroparalytic events that occur following receipt of these two rabies vaccines are related to an immune response to admixed neural constituents in the inoculum.