Time delay in non-lethal infectious diseases

The effects of the incubation period q on the dynamics of non-lethal infectious diseases in a fixed-size population are studied by means of a delay differential equation model. It is noted that the ratio between the quantity q and the time τ for recovering from the illness plays an impor-tant role in the onset of the epidemic break-through. An approximate analytic expression for the solution of the delay differential equation governing the dynamics of the system is pro-posed and a comparison is made with the clas-sical SEIR model