Fig 1. Seasonality of influenza epidemics in Hong Kong.

Upper panel: infection rate time series for the three influenza viruses (A). Middle panel: annual cycles for A(H1N1) (B), A(H3N2) (C), and B (D). Color lines show infection rates for individuals years during Jan 1998 –July 2018; lighter colors show earlier years and darker colors for later years. Thick black lines show the mean excluding 2009 for the A(H1N1) pandemic. Lower panel: estimated seasonal R₀ cycles for A(H1N1) (E), A(H3N2) (F), and B (G).