Annually a total of 100 cases were introduced into each one year age band between the ages of 5 and 50 years. Children under 5 years old are less likely to be the first individuals infected in an epidemic [26]. Adults over 50 years of age also tend not to be the first infected, due to pre-existing immunity to circulating strains. As a check for coding errors and of the model’s structure and numerical solution, the RAS model was independently recoded as a set of partial differential equations (PDEs) and run using the baseline set of parameter values for influenza A. Firstly, numerical solutions of the RAS model and the PDE model were compared visually. Secondly,

the PDE model population was assumed to selleck mix in a homogeneous fashion and the model was integrated over age to derive an ordinary differential equation (ODE) system in time only. GSI-IX chemical structure An equilibrium analysis was performed on the ODE system and the numerical solution was compared with that of the PDE system integrated over time. Thirdly, the PDE model was considered at the time-independent equilibrium, resulting in a set of ODEs in age. This system was solved numerically and compared with the equilibrium age profile generated from the

full PDE system. The details of this analysis are included in Appendix B. The simulated age stratified proportion of the population infected was checked for face validity against

corresponding data from the Tecumseh study performed in 1978 [27] and [28]. The Tecumseh data should only be considered as a rough guide as the data are old and probably underestimate the proportion infected, especially in young children [27]. Additionally, population density and mixing patterns are likely to have changed over the intervening years. In order to translate incident infections into clinical outcomes, the model was used to estimate the mean annual number of new influenza infections, prior to the introduction of any new whatever interventions. An estimate of the annual number of each clinical outcome was taken from a previous study of the burden of influenza [3]. Dividing the mean annual number of each outcome by the mean annual number of infections provided an age stratified estimate of the probability of a new infection leading to a general practice consultation, hospitalisation or death. The burden of influenza was measured using the age stratified mean annual number of general practice consultations, hospitalisations and deaths over 15 years, from 2009 to 2024 (Appendix A). Current practice in England and Wales involves vaccinating everyone over the age of 65 years and anyone between 6 months and 64 years of age in a defined risk group [29] with a trivalent inactivated vaccine (TIV). This policy was introduced in 2000.