Fig. 2.

Relative timing of positive influenza samples of type A and type B. (A and B) For each state and influenza season (excluding the 2019 season), we identify the week with the largest number of positive type A samples per 100,000 individuals. We then recenter these peak weeks at week zero and consider other weeks of each season relative to their corresponding peak A reference week. We then summarize the distribution of positive samples in each relative week (median in black, IQR and 80% CI in dark and light shading, respectively). In C and D, we repeat this analysis for the (incomplete) 2019 season (and thus contain fewer observations). A and C show type A (red) and B and D show type B (blue). See also SI Appendix, Fig. S9. (E) Generalized additive model fit showing, for each season (indicated by color), the expected weekly difference (per 100,000 individuals) in positive samples between types A and B (gray shading shows 95% CI). Observed values for each week–state pair are displayed for each season in SI Appendix, Fig. S11. (F) Phase lag between weekly type A and type B samples for weeks within seasons 2010 to 2019 (median, IQR indicated by boxplot). Dominant periods for each time series were calculated using wavelet transform, with relevant phases extracted from filtered time series using a low-pass filter with cutoff period of 1 y (Materials and Methods). (G) Performance of season-specific GAMs of weekly proportion of positive samples that are type B, displayed as model residuals (the difference between observed and predicted proportions; Materials and Methods and SI Appendix, Figs. S12 and S13).