Abstract
BackgroundSimulation models of influenza spread play an important role for pandemic preparedness. However, as the world has not faced a severe pandemic for decades, except the rather mild H1N1 one in 2009, pandemic influenza models are inherently hypothetical and validation is, thus, difficult. We aim at reconstructing a recent seasonal influenza epidemic that occurred in Switzerland and deem this to be a promising validation strategy for models of influenza spread.MethodsWe present a spatially explicit, individual-based simulation model of influenza spread. The simulation model bases upon (i) simulated human travel data, (ii) data on human contact patterns and (iii) empirical knowledge on the epidemiology of influenza. For model validation we compare the simulation outcomes with empirical knowledge regarding (i) the shape of the epidemic curve, overall infection rate and reproduction number, (ii) age-dependent infection rates and time of infection, (iii) spatial patterns.ResultsThe simulation model is capable of reproducing the shape of the 2003/2004 H3N2 epidemic curve of Switzerland and generates an overall infection rate (14.9 percent) and reproduction numbers (between 1.2 and 1.3), which are realistic for seasonal influenza epidemics. Age and spatial patterns observed in empirical data are also reflected by the model: Highest infection rates are in children between 5 and 14 and the disease spreads along the main transport axes from west to east.ConclusionsWe show that finding evidence for the validity of simulation models of influenza spread by challenging them with seasonal influenza outbreak data is possible and promising. Simulation models for pandemic spread gain more credibility if they are able to reproduce seasonal influenza outbreaks. For more robust modelling of seasonal influenza, serological data complementing sentinel information would be beneficial.
Highlights
Simulation models of influenza spread play an important role for pandemic preparedness
We succeeded in compiling a simulation model, which is capable of reproducing main characteristics of the 2003/2004 H3N2 epidemic in Switzerland and seasonal influenza in general
We were able to reproduce the following characteristics: 1.) The shape of the epidemic curve was similar in model and extrapolated Swiss sentinel data; overall infection rates and reproduction numbers were in the same range as reported for several outbreaks in various countries
Summary
Simulation models of influenza spread play an important role for pandemic preparedness. In agreement with the prevailing view in philosophy of science, we see model validation as a rather non-algorithmic, but argumentative process [15,16]: Achieving a good statistical fit between a simulated and an empirical epidemic curve does not automatically mean that the model is valid. Instead, it has to be agreed upon which aspects of reality shall be reproduced and what reproduction exactly means. Models forecasting future events cannot be checked against empirical data, but applying such a model successfully to past events provides some certainty that the model is valid per se and can be used for the comparative assessment of different scenarios including interventions
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