title: Risks of neurological and immune-related diseases, including narcolepsy, after vaccination with Pandemrix: a population- and registry-based cohort study with over 2 years of follow-up.
abstract: OBJECTIVE
  To investigate the association between vaccination with Pandemrix and risk of selected neurological and immune-related diseases including narcolepsy.
  
  
  METHODS
  Population-based prospective cohort study using data from regional vaccination registries and national health registries.
  
  
  METHODS
  Seven healthcare regions in Sweden comprising 61% of the Swedish population.
  
  
  METHODS
  Study population of 3,347,467 vaccinated and 2,497,572 nonvaccinated individuals (vaccination coverage ≈ 60%) followed between 2009 and 2011 for 6.9 million person-years after exposure and 6.0 million person-years without exposure.
  First recorded diagnosis of neurological and immune-related diseases. Relative risks [hazard ratios (HRs) with 95% confidence intervals (CIs)] assessed using Cox regression, adjusted for covariates.
  
  
  RESULTS
  For all selected neurological and immune-related outcomes under study, other than allergic vaccine reactions (for which we verified an expected increase in risk) and narcolepsy, HRs were close to 1.0 and always below 1.3. We observed a three-fold increased risk of a diagnosis of narcolepsy (HR: 2.92, 95% CI: 1.78-4.79; that is, four additional cases per 100,000 person-years) in individuals ≤ 20 years of age at vaccination and a two-fold increase (HR: 2.18, 95% CI: 1.00-4.75) amongst young adults between 21 and 30 years of age. The excess risk declined successively with increasing age at vaccination; no increase in risk was seen after 40 years of age.
  
  
  CONCLUSIONS
  For a large number of selected neurological and immune-related diseases, we could neither confirm any causal association with Pandemrix nor refute entirely a small excess risk. We confirmed an increased risk for a diagnosis of narcolepsy in individuals ≤ 20 years of age and observed a trend towards an increased risk also amongst young adults between 21 and 30 years.
authors.affiliation: Medical Products Agency, Uppsala, Sweden.
authors.forename: I
authors.initials: I
authors.lastname: Persson
authors.forename: F
authors.initials: F
authors.lastname: Granath
authors.forename: J
authors.initials: J
authors.lastname: Askling
authors.forename: J F
authors.initials: JF
authors.lastname: Ludvigsson
authors.forename: T
authors.initials: T
authors.lastname: Olsson
authors.forename: N
authors.initials: N
authors.lastname: Feltelius
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D020274:Autoimmune Diseases of the Nervous System / Q000139:chemically induced; D002648:Child; D002675:Child, Preschool; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007154:Immune System Diseases / Q000139:chemically induced*; D007223:Infant; D007252:Influenza Vaccines / Q000008:administration & dosage / Q000009:adverse effects*; D008297:Male; D008875:Middle Aged; D009290:Narcolepsy / Q000139:chemically induced*; D009422:Nervous System Diseases / Q000139:chemically induced*; D016017:Odds Ratio; D016016:Proportional Hazards Models; D011446:Prospective Studies; D012042:Registries; D012306:Risk; D013548:Sweden / Q000453:epidemiology; D014611:Vaccination / Q000009:adverse effects*
chemical_list: D007252:Influenza Vaccines; C556153:pandemrix
keywords: Pandemrix; cohort study; narcolepsy; neurological/immune-related diseases