Fig. 6: Affect of seasonal forcing on coupled dynamics.

Bifurcation diagrams for RSV (A) and hMPV (B) asymptotic dynamics in the fitted model. The prevalence of each pathogen on the 12th week of the year (y-axis) is shown as the amplitude of seasonal forcing increases. For hMPV, a second bifurcation diagram is shown for the worst-case vaccination scenario (gray dots), where RSV infection does not protect against subsequent hMPV infection at all (c = 0). Seasonal regimes of the fitted model are shown with purple bars at the top of each bifurcation diagram (annual: dark purple, biennual: medium purple, 3-year cycle and chaotic regimes: light purple). Dotted vertical lines correspond to seasonal forcing values in three example time series shown in (C). In each example, equilibrium dynamics for RSV (green) and hMPV (orange) are shown, where hMPV dynamics in the fitted model (solid lines) are contrasted to the worst-case vaccination scenario (dashed lines).