In what follows we restrict our attention to the case of n~3, m 1,2~m and m 3~0 , allowing us to model two routes of adaptation with opposite and distinct characteristics while minimising the overall complexity in number of required strains. For both routes of adaptation, the first, wildtype strain has very low transmissibility, the third has pandemic potential, and the second strain has intermediate transmissibility. This intermediate transmissibility is not enough to sustain the novel pathogen within the human host population, but secondary infections by humans are possible. Thus we have a 1 va 2 v1. Finally, the human adapted strain has a reproductive number a 3 w1. Further, we assume an identical mean infectious period for all strains.