Abstract:
An epidemic is usually a large and short term outbreak of disease. A disease is called endemic if it persists in the population for a long period of time. In this paper we introduce a model for some diseases which have temporary immunity. It means after recovery, there is immunity but it is not permanent. In this disease, the people are divided into Some groups, susceptible, infective, immune and dead people. The spread of an infectious disease involves not only disease factors such as an infectious agent, mode of transmission, latent period, infection period. It is to be noted that we pay attention to people who are born or die because of any reason except for the disease. Then we get the equilibrium point and prove it is unstable.
