Figure 2: Preferential mixing given a single child index case. The hypothetical population consists of 10 children (left) and 10 adults (right) with equal susceptibility and infectiousness. We consider an introduction of a single child index case who has a potential to cause 8 secondary transmissions. Panels (a)–(c) illustrate contacts generated by the child index case with different , proportion of within-group contacts, being 0, 0.5 and 1.0, respectively. With (i.e., random mixing), four edges extend to child susceptibles and the other four to adult susceptibles. Nevertheless, with , additional two edges are reserved for within-child mixing and only the remaining two are connected to adult susceptibles. With (i.e., fully assortative mixing), all edges are connected with child susceptibles.