Pulse vaccination of an SEIR epidemic model with time delay

Pulse vaccination is an effective strategy for the elimination of infectious diseases. A delayed epidemic model with pulse vaccination is formulated in this paper. It is proved that the disease-free periodic solution is globally attractive if the vaccination rate is larger than θ*θ*, and the disease is uniformly persistent if the vaccination rate is less than θ*θ*. The permanence of the model is investigated analytically. Our results indicate that large vaccination rate or short pulse of vaccination or long latent period is sufficient condition for the extinction of the disease.