Useful concept in predicting when epidemic will pass. Attenuation of virulence . Well-studied example was myxoma virus in Australian rabbit population. Rabbits introduced to Australia in 1859, quickly became major pest, no natural predators. Epidemic cycles .
Many epidemics occur in more or less predictable cycles.
As new kids entered large school population, virus spread during school year, until every kid was immune and epidemic dropped off. Next fall, new population of susceptible individuals entered, new epidemic outbreak. Propagation of Diseases Reservoirs Where disease is typically found. Important to know in order to control. May take some detective work.