Impact of assortativity and of school term vs. school holidays. Global invasion threshold R
* as a function of the across-groups mixing ε and of contacts ratio η, for the reproductive number estimated during school holidays (R
0 = 1.05, panel A) and school term (R
0 = 1.4, panel B), based on contact data in the UK . Here we fix the children fraction of the population α to its European average value. The grey area indicates the extinction phase where R
* < 1, whereas the colored area refers to the region of the parameter phase space that is above the threshold condition. The rectangular box indicates the area corresponding to the European intervals for the parameters ε and η. The cases for Italy (ε = 0.08, η = 0.62), United Kingdom (ε = 0.11, η = 0.75), and Finland (ε = 0.09, η = 0.79) are highlighted.