Figure 4.

Bifurcation delay can lead to epidemics with greater peak prevalence, although this effect depends on the life-history parameters of the system. Panels show peak epidemic prevalence by stochastic realizations of bifurcation delay (x-axis on log-scale). Symbols and line types represent three different infectious periods, approximating three important childhood diseases (5 days for measles, 9 days for chickenpox, 22 days for pertussis). Lines are loess smooths added for visual clarity. Colour represents the ratio of b to a, which describes how quickly R₀ changes relative to how frequently imported infections occur in a system. Symbols are positioned at the median of the x- and y-axes for each combination of life-history parameters. Panels show four different initial population sizes (N₀ = 500, 1000, 5000 and 10 000). The relationship between delay and peak infection prevalence depends on how quickly R₀ increases, which is governed by the sweep rate, mean infectious period and population size. (Online version in colour.)