To assess the quality of fit of the model behaviour to the data, we compare the distribution of key features in the time-series data with those generated by the epidemic model using the Kullback-Leibler (KL) information distance. We use normal distributions to characterize the empirical distributions of AAR and epidemic duration across a number of years. As discussed above, ignorance of the reporting rate makes it hard to know the underlying 'real' infection rate and also makes it difficult to compare reported incidence collected under different surveillance systems. In order to compare the data from the UK and France, we assume constant reporting rates for the UK and French surveillance systems, respectively, and scale the reported values linearly such that each has a mean AAR of 15 per cent (see the electronic supplementary material). Both dataset yield standard deviations of around 35 per cent of mean value for AAR and 11 + 2 weeks for epidemic duration.