In this paper, the effect of time delay on an SEIR epidemic model with saturated incidence rate is investigated. The model has two equilibria, namely, a disease-free equilibrium and an endemic equilibrium. The threshold value of the model, which is called the basic reproduction number, is derived. The results show that for any time delay if the basic reproduction number is less than unity, the disease-free equilibrium is locally asymptotically stable whereas if it is greater than unity, the endemic equilibrium is locally asymptotically stable. Numerical simulations are presented to illustrate the analytical results.
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