OBJECTIVES: To assess the incidence of narcolepsy between January 2000 and 
December 2010 in children in western Sweden and its relationship to the 
Pandemrix vaccination, and to compare the clinical and laboratory features of 
these children.
METHODS: The children were identified from all local and regional pediatric 
hospitals, child rehabilitation centers, outpatient pediatric clinics, and 
regional departments of neurophysiology. Data collection was performed with the 
aid of a standardized data collection form, from medical records and telephone 
interviews with patients and parents. The laboratory and investigational data 
were carefully scrutinized.
RESULTS: We identified 37 children with narcolepsy. Nine of them had onset of 
symptoms before the H1N1 vaccination and 28 had onset of symptoms in 
relationship to the vaccination. The median age at onset was 10 years. All 
patients in the postvaccination group were positive for human leukocyte antigen 
(HLA)-DQB1*0602. Nineteen patients in the postvaccination group, compared with 
one in the prevaccination group, had a clinical onset that could be dated within 
12 weeks.
CONCLUSION: Pandemrix vaccination is a precipitating factor for narcolepsy, 
especially in combination with HLA-DQB1*0602. The incidence of narcolepsy was 25 
times higher after the vaccination compared with the time period before. The 
children in the postvaccination group had a lower age at onset and a more sudden 
onset than that generally seen.