title: AS03 adjuvanted AH1N1 vaccine associated with an abrupt increase in the incidence of childhood narcolepsy in Finland.
abstract: BACKGROUND
  Narcolepsy is a chronic sleep disorder with strong genetic predisposition causing excessive daytime sleepiness and cataplexy. A sudden increase in childhood narcolepsy was observed in Finland soon after pandemic influenza epidemic and vaccination with ASO3-adjuvanted Pandemrix. No increase was observed in other age groups.
  
  
  METHODS
  Retrospective cohort study. From January 1, 2009 to December 31, 2010 we retrospectively followed the cohort of all children living in Finland and born from January 1991 through December 2005. Vaccination data of the whole population was obtained from primary health care databases. All new cases with assigned ICD-10 code of narcolepsy were identified and the medical records reviewed by two experts to classify the diagnosis of narcolepsy according to the Brighton collaboration criteria. Onset of narcolepsy was defined as the first documented contact to health care because of excessive daytime sleepiness. The primary follow-up period was restricted to August 15, 2010, the day before media attention on post-vaccination narcolepsy started.
  
  
  RESULTS
  Vaccination coverage in the cohort was 75%. Of the 67 confirmed cases of narcolepsy, 46 vaccinated and 7 unvaccinated were included in the primary analysis. The incidence of narcolepsy was 9.0 in the vaccinated as compared to 0.7/100,000 person years in the unvaccinated individuals, the rate ratio being 12.7 (95% confidence interval 6.1-30.8). The vaccine-attributable risk of developing narcolepsy was 1:16,000 vaccinated 4 to 19-year-olds (95% confidence interval 1:13,000-1:21,000).
  
  
  CONCLUSIONS
  Pandemrix vaccine contributed to the onset of narcolepsy among those 4 to 19 years old during the pandemic influenza in 2009-2010 in Finland. Further studies are needed to determine whether this observation exists in other populations and to elucidate potential underlying immunological mechanism. The role of the adjuvant in particular warrants further research before drawing conclusions about the use of adjuvanted pandemic vaccines in the future.
authors.affiliation: Department of Vaccines and Immune Protection, National Institute for Health and Welfare, Helsinki, Finland. hanna.nohynek@thl.fi
authors.forename: Hanna
authors.initials: H
authors.lastname: Nohynek
authors.forename: Jukka
authors.initials: J
authors.lastname: Jokinen
authors.forename: Markku
authors.initials: M
authors.lastname: Partinen
authors.forename: Outi
authors.initials: O
authors.lastname: Vaarala
authors.forename: Turkka
authors.initials: T
authors.lastname: Kirjavainen
authors.forename: Jonas
authors.initials: J
authors.lastname: Sundman
authors.forename: Sari-Leena
authors.initials: SL
authors.lastname: Himanen
authors.forename: Christer
authors.initials: C
authors.lastname: Hublin
authors.forename: Ilkka
authors.initials: I
authors.lastname: Julkunen
authors.forename: Päivi
authors.initials: P
authors.lastname: Olsén
authors.forename: Outi
authors.initials: O
authors.lastname: Saarenpää-Heikkilä
authors.forename: Terhi
authors.initials: T
authors.lastname: Kilpi
mesh_terms: D000276:Adjuvants, Immunologic / Q000008:administration & dosage; D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D016208:Databases, Factual; D005387:Finland / Q000453:epidemiology; D006801:Humans; D015994:Incidence; D053118:Influenza A Virus, H1N1 Subtype; D007252:Influenza Vaccines / Q000009:adverse effects* / Q000276:immunology; D008875:Middle Aged; D009290:Narcolepsy / Q000453:epidemiology* / Q000209:etiology*; D012189:Retrospective Studies; D014611:Vaccination; D055815:Young Adult
chemical_list: D000276:Adjuvants, Immunologic; D007252:Influenza Vaccines