Figure 2A and B shows the fraction of frequency trajectories in HA and NA that either have fixed, were lost or remained active as a function of the time elapsed since they were first seen above 25% frequency for A/H3N2 and A/H1N1pdm, respectively. Most mutations are either lost or become fixed after 2–3 years, with very few trajectories remaining active after 5 years. This time scale of 2–3 years is consistent with the typical coalescence time observed in phylogenetic trees of A/H3N2 influenza (Rambaut et al. 2008; Yan et al. 2019). Here, XK is linked to influenza.