Size. The most sophisticated and general way to obtain exact results for the expected final size of a major outbreak on a network is called the susceptibility set argument and the most general version is currently given by Ball et al. [117] . We give an example of these kind of arguments from Diekmann et al. [123] , who consider the simpler case of a network in which each individual has n contacts. Where there is a probability p of infection passing across a given network link (so for transmission and recovery at rates τ and γ, resp., p = τ/(τ + γ)), the probability that an individual avoids infection is given by