Epidemics in populations with community structure show a distinct dynamical pattern depending on the extent of community structure. In networks with strong community structure, an infected individual is more likely to infect members of the same community than members outside of the community. Thus, in a network with strong community structure, local outbreaks may die out before spreading to other communities, or they may spread through various communities in an almost serial fashion, and large epidemics in populations with strong community structure may therefore last for a long time. Correspondingly, the incidence rate can be very low, and the number of generations of infection transmission can be very high, compared to the explosive epidemics in populations with less community structure (Figures 2a and 2b ). On average, epidemics in networks with strong community structure exhibit greater variance in final size (Figures 2c and 2d) , a greater number of small, local outbreaks that do not develop into a full epidemic, and a higher variance in the duration of an epidemic.