title: Essential epidemiological mechanisms underpinning the transmission dynamics of seasonal influenza.
abstract: Seasonal influenza has considerable impact around the world, both economically and in mortality among risk groups, but there is considerable uncertainty as to the essential mechanisms and their parametrization. In this paper, we identify a number of characteristic features of influenza incidence time series in temperate regions, including ranges of annual attack rates and outbreak durations. By constraining the output of simple models to match these characteristic features, we investigate the role played by population heterogeneity, multiple strains, cross-immunity and the rate of strain evolution in the generation of incidence time series. Results indicate that an age-structured model with non-random mixing and co-circulating strains are both required to match observed time-series data. Our work gives estimates of the seasonal peak basic reproduction number, R(0), in the range 1.6-3. Estimates of R(0) are strongly correlated with the timescale for waning of immunity to current circulating seasonal influenza strain, which we estimate is between 3 and 8 years. Seasonal variation in transmissibility is largely confined to 15-30% of its mean value. While population heterogeneity and cross-immunity are required mechanisms, the degree of heterogeneity and cross-immunity is not tightly constrained. We discuss our findings in the context of other work fitting to seasonal influenza data.
authors.affiliation: MRC Centre for Outbreak Analysis and modelling, Department of Infectious Disease Epidemiology, Imperial College, London W2 1PG, UK. j.truscott@imperial.ac.uk
authors.forename: James
authors.initials: J
authors.lastname: Truscott
authors.forename: Christophe
authors.initials: C
authors.lastname: Fraser
authors.forename: Simon
authors.initials: S
authors.lastname: Cauchemez
authors.forename: Aronrag
authors.initials: A
authors.lastname: Meeyai
authors.forename: Wes
authors.initials: W
authors.lastname: Hinsley
authors.forename: Christl A
authors.initials: CA
authors.lastname: Donnelly
authors.forename: Azra
authors.initials: A
authors.lastname: Ghani
authors.forename: Neil
authors.initials: N
authors.lastname: Ferguson
mesh_terms: D000367:Age Factors; D000956:Antigens, Viral / Q000276:immunology; D004196:Disease Outbreaks; D006801:Humans; D007251:Influenza, Human / Q000453:epidemiology* / Q000635:transmission; D018448:Models, Immunological; D011157:Population Dynamics; D012307:Risk Factors; D012621:Seasons
chemical_list: D000956:Antigens, Viral