OBJECTIVES: To determine the prevalence of Dravet syndrome, an epileptic 
encephalopathy caused by SCN1A-mutations, often with seizure onset after 
vaccination, among infants reported with seizures following vaccination. To 
determine differences in characteristics of reported seizures after vaccination 
in children with and without SCN1A-related Dravet syndrome.
METHODS: Data were reviewed of 1,269 children with seizures following 
immunization in the first two years of life, reported to the safety surveillance 
system of the Dutch national immunization program between 1 January 1997 and 31 
December 2006. Selective, prospective follow-up was performed of children with 
clinical characteristics compatible with a diagnosis of Dravet syndrome.
RESULTS: In 21.9% (n = 279) of children, a diagnosis of Dravet syndrome could 
not be excluded based on available clinical data (median age at follow-up 16 
months). Additional follow-up data were obtained in 83.9% (n = 234) of these 
children (median age 8.5 years). 15 (1.2% of 1,269; 95%CI:0.6 to 1.8%) children 
were diagnosed with SCN1A-related Dravet syndrome. Of all reported seizures 
following vaccinations in the first year of life, 2.5% (95%CI:1.3 to 3.6%) were 
due to SCN1A-related Dravet syndrome, as were 5.9% of reported seizures 
(95%CI:3.1 to 8.7%) after 2(nd) or 3(rd) DTP-IPV-Hib vaccination. Seizures in 
children with SCN1A-related Dravet syndrome occurred more often with a body 
temperature below 38.5°C (57.9% vs. 32.6%, p = 0.020) and reoccurred more often 
after following vaccinations (26.7% vs. 4.0%, p = 0.003), than in children 
without a diagnosis of SCN1A-related Dravet Syndrome.
CONCLUSIONS: Although Dravet syndrome is a rare genetic epilepsy syndrome, 2.5% 
of reported seizures following vaccinations in the first year of life in our 
cohort occurred in children with this disorder. Knowledge on the specific 
characteristics of vaccination-related seizures in this syndrome might promote 
early diagnosis and indirectly, public faith in vaccination safety.