The impact of evolutionary constraints on influenza dynamics.

Existing mathematical models of drift typically assume that influenza A is free to change its antigenic properties without any fitness cost in other respects. This paper asks what might be the impact of antigenic mutations being bound to fitness cost. The effect on drift is explored via a mathematical model. This paper also offers some novel features for multi-strain modeling. In contrast to the unconstrained drift models, this system can exhibit both drift-like patterns and single strain dynamics. These can occur for the same parameter values: a bistable system where it is possible to switch between these behaviours. This raises some important prospects for vaccination strategies, particularly pausing influenza drift.