Impact of age-specific travel behavior and age profile. A: Global invasion threshold R
* as a function of the across-groups mixing ε for the cases of Italy, United Kingdom, and Finland, assuming R
0 = 1.05. The solid colored lines correspond to the cases when only adults travel (r = 0) and the dashed colored lines to the cases when a percentage of 7% of passengers belongs to the children class. The continuous horizontal line indicates the threshold condition R
* = 1. B: Global invasion threshold R
* as a function of the across-groups mixing ε: comparison between Europe (α = 0.20, η = 0.79) and Mexico (α = 0.32, η = 0.32). Here we consider R
0 = 1.05 and R
0 = 1.4, assuming r = 0.