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The impact of national vaccination policy changes on influenza incidence in the Netherlands.

McDonald, S.A., Asten, L. van, Hoek, W. van der, Donker, G.A., Wallinga, J. The impact of national vaccination policy changes on influenza incidence in the Netherlands. Influenza and Other Respiratory Viruses: 2016, 10(2), 76-85
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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 targetting 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 targetting ≥65 year-olds, for whom vaccination coverage was already rising before the policy change. (aut. ref.)
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