Published Online: 15 JUL 2005
Copyright © 2005 John Wiley & Sons, Ltd
Encyclopedia of Biostatistics
How to Cite
Ball, F. 2005. Epidemic Thresholds. Encyclopedia of Biostatistics.
- Published Online: 15 JUL 2005
This article gives an overview of the threshold behavior of epidemic models, focusing primarily on stochastic closed population models. A key parameter is the reproduction number R0 of an epidemic. For a broad range of models, branching process theory is used to show that an epidemic initiated by a trace of infection in a large population can take off only if R0 is larger than one. These models assume either a homogeneous population or a stratified population in which all the subpopulations are large. Models for the spread of an epidemic among a population partitioned into a large number of small households, or among a spatially configured population, are also considered. In both of these cases R0 no longer provides a good indicator as to whether an epidemic can take off. The article closes with a brief discussion of the threshold and long-term behaviors of open population models, which incorporate demographic effects.
- epidemic model;
- threshold theorem;
- branching process;
- reproduction number;
- critical vaccination coverage;
- structured populations;
- closed and open populations;
- endemic behavior