FIG. 1.

Outbreak size $1-S_t$ for a SIR system having evolved until time $t=100$, vs the parameter defining the threshold: $\beta /\gamma$, when including memory effects. Each curve corresponds to a different value of $\alpha$, as indicated in the inset. As $\alpha$ decreases, the epidemic threshold ${(\beta /\gamma )}_c$ shifts to higher values.