24 The importance of offering influenza vaccination in pregnancy was recently emphasised by the World Health Organisation who identified pregnant women as the highest priority group for vaccination.2 However coverage in pregnant women in England

is poor only reaching 25.5% in those without co-morbidities in 2011/12.20 There were marked differences between age groups in the ratio of consultation rates in general practice to hospital admission rates for influenza (Table 4). Consultation rates will not only reflect the underlying infection rate in that age group but also the propensity to consult for an influenza-like-illness if symptomatically infected. Similarly, hospital admission rates will reflect the age-specific severity profile as well as the age-specific

Fluorouracil incidence of infection. Quantifying PFT�� the relationship between health care outcomes and the underlying infection rate in each age group is essential for building influenza transmission models that can assess the overall population impact of different vaccination polices. Estimation of age-specific influenza infection rates requires data from serological studies conducted before and after the influenza season. The value of seroepidemiology was recognised as a result of the H1N1 (2009) pandemic25 but has not been systematically applied to seasonal influenza. The strength of our study is that it enables a comparison of the influenza-attributable morbidity between age groups and the effect of underlying co-morbidities within an age group. Also, by using data from eight consecutive years, our estimates will reflect the

variation in influenza incidence and severity between seasons. Our regression method uses the year-to-year changes in the timing of the influenza season as well as in the other respiratory pathogens that are more prevalent in winter. Thus it also allows the burden of disease attributable to influenza to be compared with other respiratory PLEKHM2 pathogens such as respiratory syncytial virus and S. pneumoniae. It shows that together these latter two pathogens are responsible for around 60% all attributed hospital admitted acute respiratory illness in both risk and non-risk individuals. Our analysis also identified H. influenzae and parainfluenza as important pathogens in individuals with underlying co-morbidities. A potential limitation of this work is that we restricted our mortality analyses to patients with acute respiratory illness who die in hospital to allow derivation of case fatality rates for those in high-risk groups compared with non-risk individuals. This was essential for the cost-effectiveness analysis that was undertaken to evaluate the effect of different extensions to the current risk-based influenza vaccination programme3 and will ensure that the results are conservative.