An association between DTP vaccination and onset of seizures in 40 patients diagnosed with Dravet syndrome was investigated by retrospective analysis of medical and vaccination records at Heidelberg Hospital, Victoria, Australia. Patients with mutations in SCN1A whose first seizure was a convulsion were separated into 2 groups, those whose first seizure occurred on the day of or day after vaccination (n=12) (the vaccination-proximate group), and those with seizure onset 2 days or more after vaccination (n=25) or before vaccination (n=3) (the vaccination-distant group). Mean age at seizure onset was 18.4 weeks (SD 5.9) in the vaccination-proximate group and 26.2 weeks (SD 8.1) in the vaccination-distant group (difference p=0.004). Intellectual outcome, subsequent seizure type, and mutation type were similar in the two groups (p values >0.3). Intellectual outcome did not differ between patients who received vaccinations after seizure onset and those who did not. Vaccination might trigger earlier onset of seizures in children with SCN1A mutations and susceptibility to Dravet syndrome, but, by post-hoc analysis of data, vaccinations before or after onset of Dravet syndrome do not affect intellectual outcome. 
COMMENT. Seizures in Dravet syndrome (DS) begin in the first year, usually at or around 6 months of age. Early seizures are typically prolonged and associated with fever or infection. Known seizure triggers include, in addition to fever and infection, hot water bath, and photic or pattern stimulation. Mutations in the SCN1A gene are found in 67% to 86% of DS cases. (Dravet C et al, 1982, 2005;). 
Wiznitzer M, in an editorial , comments that the study by Mcintosh and colleagues has limitations but it attempts to introduce science over speculation and bias in the question and controversy of pertussis vaccination and encephalopathy. Although 12 individuals with DS and a first seizure within 2 days of whole cell or acellular DTP had earlier onset than the 28 with a first seizure before or more distant from vaccination, their clinical outcome, including cognitive disability, was not different, and no worsening occurred in individuals who received further vaccinations. Both authors conclude that outcome is determined by the underlying disorder and not by proximity to vaccine administration.