title: The impact of national vaccination policy changes on influenza incidence in the Netherlands.
abstract: BACKGROUND
  We assessed the impact of two major modifications of the Dutch National Influenza Prevention Programme--the introduction in 1997 of free-of-charge vaccination to persons aged ≥65 years and to high-risk groups (previously only advised, and not free of charge), and the lowering of the eligible age to 60 years in 2008--on the estimated incidence of influenza infection leading to influenza-like illness (ILI).
  
  
  METHODS
  Additive negative-binomial segmented regression models were fitted to ILI data from GP sentinel surveillance in two-eight-season intervals (1993/4 to 2000/1, 2004/5 to 2011/12, comparing pre- and post-policy-change periods within each interval), with laboratory virological reporting of samples positive for influenza or other ILI-causing pathogens as covariates.
  
  
  RESULTS
  For the 2008 policy change, there was a significant step decrease in influenza contribution considering all ages (=-111 per 100 positives; 95% CI: -162, -65·0), <60 years and 60-64 years age groups (B = -92·1 per 100; 95% CI: -134, -55·5; B = -5·2; 95% CI: -10·3, -1·2, respectively). There was no evidence for a decrease associated with the 1997 policy change targeting the ≥65 years age group.
  
  
  CONCLUSIONS
  In the Netherlands, a 56% reduction in influenza contribution was associated with the 2008 policy targeting 60-64 year-olds, but there was no effect of the earlier policy targeting ≥65-year-olds, for whom vaccination coverage was already rising before the policy change.
authors.affiliation: Centre for Infectious Disease Control, National Institute for Public Health and the Environment, Bilthoven, The Netherlands.
authors.forename: Scott A
authors.initials: SA
authors.lastname: McDonald
authors.affiliation: Centre for Infectious Disease Control, National Institute for Public Health and the Environment, Bilthoven, The Netherlands.
authors.forename: Liselotte
authors.initials: L
authors.lastname: van Asten
authors.affiliation: Centre for Infectious Disease Control, National Institute for Public Health and the Environment, Bilthoven, The Netherlands.
authors.forename: Wim
authors.initials: W
authors.lastname: van der Hoek
authors.affiliation: NIVEL Primary Care Database, Sentinel Practices, Utrecht, The Netherlands.
authors.forename: Gé A
authors.initials: GA
authors.lastname: Donker
authors.affiliation: Centre for Infectious Disease Control, National Institute for Public Health and the Environment, Bilthoven, The Netherlands.
authors.forename: Jacco
authors.initials: J
authors.lastname: Wallinga
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006291:Health Policy; D006801:Humans; D017589:Immunization Programs; D015994:Incidence; D007252:Influenza Vaccines; D007251:Influenza, Human / Q000453:epidemiology / Q000517:prevention & control* / Q000821:virology; D008297:Male; D008875:Middle Aged; D009426:Netherlands / Q000453:epidemiology; D012621:Seasons; D018571:Sentinel Surveillance; D014611:Vaccination / Q000706:statistics & numerical data
chemical_list: D007252:Influenza Vaccines
keywords: Influenza; influenza-like illness; statistical model; the Netherlands; vaccination policy