Toxicity of pertussis vaccine: frequency and probability of reactions.

From a file of 1127 children in whom signs of brain damage were reported after injections of vaccines containing pertussis antigen, the first 197 cases with good documentation of events were chosen for further study. In these children, 291 reactions had been reported, usually of screaming attacks (68), convulsions (87), collapse (17), or one or more of these signs (99), within 24 hours of injection. Subsequently 165 children became mentally defective and 102 had further convulsions. In 129 (65%), contraindications to vaccination were present and in 25, subsequent injections were given despite reactions to a previous injection or injections. From a mathematical model constructed from data in published reports, it is calculated that the frequency of convulsions appears to be higher by 2: 1 in vaccinated than in unvaccinated infants. In children subject to febrile or other convulsions, the frequencies may be of the same order but a second convulsion occurring only after a second or subsequent injection of vaccine is unlikely to be due to chance. The pattern of reactions and sequence of events observed in the present study and in published reports suggest an association between certain reactions to pertussis vaccine and subsequent severe brain damage, the incidence of which appears to be not less than one per fifty thousand children vaccinated during the last 20 years of mass vaccination in the United Kingdom.