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Adverse Events Associated with Childhood Vaccines: Evidence Bearing on Causality
cranial nerve palsies. Therefore, clinical diphtheria disease and tetanus disease have not been associated with seizures.
Inasmuch as DT, Td, tetanus toxoid, and DPT have been known to cause fever, they have been associated with the occurrence of acute febrile seizures. Febrile seizures alone do not lead to a residual seizure disorder. There are a paucity of case reports in the literature describing seizures (other than febrile) that have occurred in association with diphtheria and tetanus toxoids. However, several large epidemiologic studies were designed to investigate the association between receipt of DPT and acute neurologic events in children. From those studies, information regarding DT was also obtained because there was not universal acceptance of DPT. Bellman et al. (1983) examined a subset of the NCES data for a relation between the onset of infantile spasms and recent vaccination with DT and DPT. Pollock et al. (1984, 1985) and Pollock and Morris (1983) examined the relation between the onset of neurologic events (including seizures) and vaccination with DT and DPT in several different studies.
Evidence for Association
There are no data directly bearing on the biologic plausibility of a relation between diphtheria or tetanus toxoid and residual seizure disorder.
Case Reports, Case Series, and Uncontrolled Observational Studies
Three uncontrolled observational (cohort) studies provide descriptive information. The North West Thames study (Pollock and Morris, 1983 [see previous section on encephalopathy]), an uncontrolled cohort study, also offers some information regarding seizures following DT immunization. In the voluntary reporting part of the study, of 133,500 children who received a primary series of three immunizations (400,500 doses) of DT (and OPV), and 221,000 single booster doses of DT given at school entry, seven children had seizures, and all were normal on follow-up. Two of these were febrile seizures associated with respiratory illness and possible fever, and three were in children with personal or family histories of seizures. In the hospital activity analysis, of 18,000 children who received a primary series of DT (and OPV) (54,000 doses), 18 children had seizures, all of which were febrile, within 28 days of immunization. Of the children who presented with neurologic disease after DT immunization, two patients with convulsions with focal signs presenting at 22 and 24 days postimmunization, respectively, were reported. Long-term follow-up of these two patients was not presented in the report, but the relatively long period of time between