Literature regarding pertussis vaccination and risk of encephalopathy and/or epilepsy is reviewed by researchers from UCL Institute of Neurology, London, UK, and North Illinois University, DeKalb, IL, USA. Current risk estimates of vaccine-related febrile seizure are 1 per 18,496 vaccinations; afebrile seizure 1 per 76,133; and encephalopathy 0-3 per million. The rate of febrile seizures within 2 days of the present acellular vaccine is much lower than that of 1 per 2835 with previous whole-cell vaccine. 
As part of a recent study of unexplained encephalopathies in Australia, New Zealand, Canada and Scotland, Berkovic SF et al  identified 14 cases within 72 hours of pertussis vaccination, treated by child neurologists. Of these presumed vaccine-related cases, 11 had an inherited genetic defect of the SCN1A gene that corresponded to the phenotype for severe myoclonic epilepsy of infancy (SMEI, Dravet syndrome). The encephalopathy temporally associated with pertussis vaccination may, in some cases, be due to an SCN1A mutation and Dravet syndrome. This finding requires replication by further studies. 
COMMENT. Fortunately, the risk of neurologic complications of pertussis vaccine has fallen remarkably since the introduction of the acellular vaccine. With whole-cell vaccine, reports of neurologic complications, especially febrile seizures or infantile spasms, were not uncommon in US pediatric neurology practice. In the same time period, encephalopathy attributed to whooping cough was a very rare neurologic diagnosis. In vaccine related encephalopathies, a test for SMEI should be considered in the differential diagnosis.
In Australia and New Zealand, the experience is different from the US. Among 49 unimmunized infants (age 6 weeks) admitted with pertussis to the PICU at Royal Children’s Hospital, Melbourne, between 1985-2004, 63% had apnea, 18% pneumonia, and 10% had seizures. Deaths in 7 were due to pneumonia and circulatory failure . At Starship Children’s Hospital, Auckland, NZ, 72 children (<12 months old) were admitted to the PICU with pertussis from 1991-2003. Apnea and cough were presenting symptoms in 83%, 4 died and 6 had neurodevelopmental problems . In unimmunized populations, pertussis is a serious disease with complications, principally respiratory.