FIG. 3.

Order parameter $1-S_t$ for a SIR system having evolved until time $t$, when including much memory ($\alpha =0.2$). Each curve corresponds to a different finite time $t$, as indicated in the inset. The threshold values can be compared with that of the corresponding epidemic threshold for a memoryless system, i.e., when $\alpha =1$ (and $t=20$). The curves for $\alpha =1$ at $t=200$ and $t=2000$ are not drawn for better readability.