Pertussis immunization and characteristics related to first seizures in infants and children.

In a previous study in which we examined the relationship of pertussis immunization to the onset of neurologic disorders during 1967 and 1968 and during 1972 and 1973 in Denmark, there were 554 children with initial onset of epilepsy and 2158 children with first febrile convulsions. In the study population there were 112 children with epilepsy and 229 children with febrile convulsions for whom the exact date of pertussis immunization and the exact date of the onset of illness were known. We analyzed selected clinical variables by specific time intervals between pertussis immunization and the first seizure. In the children with epilepsy, no relationship was found between time of pertussis immunization and the specific variables that were examined. In contrast, the following characteristics in children with febrile seizures were significantly more common when pertussis immunization had occurred within 3 days, compared with more than 7 days of the event: first seizure more than 10 minutes in duration, the occurrence of more than one seizure, the longest seizure (when there was more than one) more than 10 minutes in duration, and the occurrence of a seizure described as focal. The lack of specific characteristics in epilepsy that had its onset in a temporal relationship to pertussis immunization is further evidence that pertussis vaccine does not cause this disorder. The cause of increased severity of febrile seizures apparently associated with pertussis immunization is unknown.