A. Epidemic onsets are earlier in seasons with increased H3 epitope distance (t − 2), but the correlation is not statistically significant. B. Epidemic peaks are earlier in seasons with increased H3 epitope distance (t − 2) and N2 epitope distance (t − 1), but correlations are not statistically significant. Seasonal epitope distance is the mean distance between strains circulating in season t and those circulating in the prior season (t − 1) or two seasons ago (t − 2). Distances are scaled to aid in direct comparison of evolutionary indicators. Point color indicates the dominant influenza A subtype based on CDC influenza season summary reports (red: A(H3N2), blue: A(H1N1), purple: A(H1N1)pdm09, orange: A(H3N2)/A(H1N1)pdm09 co-dominant). Seasonal mean epidemic onsets and peaks were fit as a function of H3 or N2 epitope distance using Gaussian GLMs (inverse link) with 1000 bootstrap resamples.