title: Effectiveness of a MF-59™-adjuvanted pandemic influenza vaccine to prevent 2009 A/H1N1 influenza-related hospitalisation; a matched case-control study.
abstract: BACKGROUND
  During the 2009 influenza A/H1N1 pandemic, adjuvanted influenza vaccines were used for the first time on a large scale. Results on the effectiveness of the vaccines in preventing 2009 influenza A/H1N1-related hospitalisation are scanty and varying.
  
  
  METHODS
  We conducted a matched case-control study in individuals with an indication for vaccination due to underlying medical conditions and/or age ≥ 60 years in The Netherlands. Cases were patients hospitalised with laboratory-confirmed 2009 A/H1N1 influenza infection between November 16, 2009 and January 15, 2010. Controls were matched to cases on age, sex and type of underlying medical condition(s) and drawn from an extensive general practitioner network. Conditional logistic regression was used to estimate the vaccine effectiveness (VE = 1 - OR). Different sensitivity analyses were used to assess confounding by severity of underlying medical condition(s) and the effect of different assumptions for missing dates of vaccination.
  
  
  RESULTS
  149 cases and 28,238 matched controls were included. It was estimated that 22% of the cases and 28% of the controls received vaccination more than 7 days before the date of onset of symptoms in cases. A significant number of breakthrough infections were observed. The VE was estimated at 19% (95%CI -28-49). After restricting the analysis to cases with controls suffering from severe underlying medical conditions, the VE was 49% (95% CI 16-69).
  
  
  CONCLUSIONS
  The number of breakthrough infections, resulting in modest VE estimates, suggests that the MF-59™ adjuvanted vaccine may have had only a limited impact on preventing 2009 influenza A/H1N1-related hospitalisation in this setting. As the main aim of influenza vaccination programmes is to reduce severe influenza-related morbidity and mortality from influenza in persons at high risk of complications, a more effective vaccine, or additional preventive measures, are needed.
authors.affiliation: Epidemiology and Surveillance Unit, Centre for Infectious Disease Control, National institute for Public Health and the Environment, Bilthoven, The Netherlands.
authors.forename: Anneke
authors.initials: A
authors.lastname: Steens
authors.forename: Eleonora G
authors.initials: EG
authors.lastname: Wijnans
authors.forename: Jeanne P
authors.initials: JP
authors.lastname: Dieleman
authors.forename: Miriam Cjm
authors.initials: MC
authors.lastname: Sturkenboom
authors.forename: Marianne Ab
authors.initials: MA
authors.lastname: van der Sande
authors.forename: Wim
authors.initials: W
authors.lastname: van der Hoek
mesh_terms: D000276:Adjuvants, Immunologic; D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D016022:Case-Control Studies; D002648:Child; D002675:Child, Preschool; D005260:Female; D006760:Hospitalization / Q000706:statistics & numerical data; D006801:Humans; D007223:Infant; D053118:Influenza A Virus, H1N1 Subtype / Q000276:immunology*; D007252:Influenza Vaccines / Q000008:administration & dosage* / Q000276:immunology; D007251:Influenza, Human / Q000453:epidemiology / Q000276:immunology / Q000517:prevention & control*; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D058873:Pandemics / Q000517:prevention & control
chemical_list: D000276:Adjuvants, Immunologic; D007252:Influenza Vaccines