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Adverse Events Associated with Childhood Vaccines: Evidence Bearing on Causality
cending pattern. About one-third of patients with GBS require assisted ventilation, but rarely is the condition fatal. In most patients there is spontaneous improvement after weeks or months, usually leading to complete recovery. The annual incidence of GBS appears to be approximately 1 per 100,000 for adults. The data are not definitive, but the annual incidence of GBS in children under age 5 years appears to be approximately the same. The annual incidence of GBS in children over age 5 years and teenagers appears to be lower. Chapter 3 contains a detailed discussion of GBS.
History of Suspected Association
In 1989, D'Cruz and coworkers reported three cases of GBS following immunization with the Hib conjugate vaccine PRP-diphtheria toxoid (PRP-D). Two children received the PRP-D vaccine alone, but the third child received DPT and OPV as well. The onset of symptoms in this child occurred 1 day following immunization. One day is too short a period of time, as described in Chapter 3, to support the notion that the GBS attack was plausibly related to the vaccination.
Evidence for Association
A general discussion of GBS and vaccination can be found in Chapter 3. There are no data specifically bearing on the biologic plausibility of a causal relation between Hib vaccines and GBS.
Case Reports, Case Series, and Uncontrolled Observational Studies
A total of seven cases labeled GBS have been described following immunization with the three Hib conjugate vaccines that are currently licensed for use in the United States. The three cases following administration of the PRP-D vaccine noted above occurred during a period when approximately 6.2 million doses of PRP-D vaccine were distributed (D'Cruz et al., 1989). None of these children were noted to have an antecedent infection. A different lot of PRP-D vaccine was used in each child.
A fourth case of GBS following vaccination with PRP-D vaccine was reported recently by Gervaix and colleagues (1993). A 4-year-old girl developed signs of GBS (progressive weakness in legs with hypotonia and complete loss of tendon reflexes, difficulty in swallowing, and bilateral facial weakness) 10 days after receiving PRP-D Hib vaccine. The report documented decreased nerve conduction velocities and prolonged distal latencies. Serological tests were negative for cytomegalovirus, herpesvirus, Epstein-Barr virus, Borrelia burgdorferi, and Campylobacter species. IgM