Administration of pertussis vaccine has been associated temporally with local and systemic reactions, including febrile convulsions. Based on the National Childhood Encephalopathy Study (NCES), a large case-controlled, epidemiologic study in Great Britain, permanent neurological disability (brain damage) has not been considered a common sequela of rare, severe, adverse neurological events temporally related to pertussis immunization. Recently, however, reassessment of this conclusion has been prompted by the following events: a review of the NCES by a workshop convened to make recommendations for a possible future United States study of the association of pertussis vaccination and serious neurological illness,1 a legal decision in Great Britain questioning the findings of NCES;2 further investigations of the role of pertussis vaccine in causation of acute and chronic neurologic illness;3-6 and continuing reassessment of recommendations for pertussis vaccination by national committees in Canada,7 Great Britain,8 and the United States. Recent reviews and editorials also have addressed this and related questions concerning adverse events attributed to pertussis vaccine.9-12
The Committee herein reports its reassessment of the role of pertussis vaccine as a cause of chronic neurological disability. In this review, the term "encephalopathy" is avoided deliberately. Definition of this term is difficult, and its use can be misleading. For example, the NCES study population was children with acute, serious neurological illness, the majority of whom had convulsions lasting 30 minutes or more.13 Thus, in assessing the nature of the relationship between pertussis immunization and neurological events, the term "acute, serious neurological illness" is considered more appropriate than "encephalopathy."