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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.

Original publication

DOI

10.1098/rsif.2011.0309

Type

Journal article

Journal

Journal of the Royal Society, Interface

Publication Date

02/2012

Volume

9

Pages

304 - 312

Addresses

MRC Centre for Outbreak Analysis and modelling, Department of Infectious Disease Epidemiology, Imperial College, London W2 1PG, UK. j.truscott@imperial.ac.uk

Keywords

Humans, Antigens, Viral, Risk Factors, Seasons, Disease Outbreaks, Age Factors, Population Dynamics, Models, Immunological, Influenza, Human