S-I-S stands for susceptible-infective-susceptible. It is a mathematical model for some infectious diseases that do not confer immunity. An S-I-S disease has the potential to become endemic, that is, approach a nonzero limit in the fractions of susceptible and infected people. The disease never goes away. The project is to find mathematical conditions that say when the disease becomes endemic. As with any model, it has limitations. It will not give us exact answers, but it will help us to see the general trends and make some important predictions.
Web page maintained by dave@hornacek.coa.edu.