Figure 6.13 Velocity of epidemic waves in Iceland for the influenza seasons 1915–16 to 1975–76. (A) Velocities of the leading edge (LE, solid lines) and following edge (FE, pecked lines) are shown as the velocity ratios, VLE and VFE, defined in Appendix Appendix 6.1: Swash–Backwash Model Equations 6.1 equation (A2). V is in the range, 0 ≤ V ≤ 1. The larger the value of V, the faster the edge. (B) The widening time gap between the two edges illustrated in (A) is confirmed in this graph which plots the average duration of each district’s epidemic wave in months. In both (A) and (B) the trend lines were determined by OLS linear regression.

Source: All influenza data based on Heilbrigðisskýrslur (Public Health in Iceland)