Background: In 2003, the World Health Assembly (WHA) issued a resolution for prevention and control of influenza pandemics and annual epidemics, which urges the European Union 25 (EU-25) Member States to (1) establish and implement strategies to increase vaccination coverage of all people at high risk, including the elderly and people with underlying disease, with the goal of attaining vaccination coverage of the elderly population of at least 50% by 2006 and 75% by 2010; (2) to assess the disease burden and economic impact of annual influenza epidemics as a basis for framing and implementing influenza prevention policies. This resolution was reinforced by the European Union (EU), where Member States agreed to make additional efforts to improve uptake on their territory in accordance with their own recommendations and to achieve the World Health Organisation (WHO) target of 75% in high risk groups before 2010. It was also noted that the changing demographic profile of the EU population would result in an increasing number of elderly people falling within the current target groups.

Objectives: To establish the number of people who may be eligible for influenza vaccination in the EU, and estimate the costs and consequences of not vaccinating this population for five EU Member States, France, Germany, Italy, Spain, and the UK.

Methods: A mathematical model has previously been developed, in which vaccine distribution data are combined with demographic and health economics data to model the public health consequences of influenza and possible intervention strategies. We have extended that model using specific EU-25 demographic data on populations at risk of influenza during the inter-pandemic period. For each country, the total population and age breakdown was calculated to estimate the percentage of the population that falls under the WHA recommendations. Other target groups for influenza vaccination were identified by analysing estimating the proportion of the population with respiratory or cardiovascular related diseases, diabetes, AIDS or transplantation, as well as health care professionals. Target population size and possible vaccination coverage rates across the EU-25 Member States, along with the potential cost and health consequence impact is estimated.

Results: For the EU-25, it was estimated that up to 49.1% of the population (or 223.4 million people) should be vaccinated against influenza. This ranged from 41.6% in Cyprus to 56.4% in the UK. There were, on average, 174 vaccine doses distributed per 1000 population within the EU-25, which leads to an average vaccination rate of the target population of 35.4% based on current supply constraints. As a consequence, up to 144.4 million people who could be considered "at risk" may not currently be vaccinated. Implementing a 100% vaccination rate programme for all risk groups across the EU-25 would lead to an estimated reduction of number of influenza cases of 7.22 million, 1.96 million reduced PCP visits for influenza treatment, 796,743 less hospital admissions and 68,537 fewer influenza related deaths for all EU-25 countries. The implementation of a 100% vaccination rate programme for all risk groups in France, Germany, Italy, Spain and UK would require an additional 1.52 billion Euro. This would result in estimated savings of 39.45 million Euro of reduced primary care visits and further savings of 1.59 billion Euro in reduced hospitalisations respectively in these countries.

Conclusions: There is a gap between current vaccination coverage and the EU recommendations. The public health consequences of low vaccination coverage include increased morbidity, hospitalisations and mortality associated with influenza-related complications. This model is a powerful tool to: (1) support EU public health officials in implementing recommendations; (2) to visualize the need for increased vaccination rates for better influenza control; (3) the consequences of low vaccine coverage.