Fig. 3.

Epidemic size contours and shading show that when ${\mathcal{R}}_0$ is close to 1, the epidemic is more strongly influenced by a reduction of $I_0$ than by a reduction of ${\mathcal{R}}_0$. For instance, if ${\mathcal{R}}_0=0.95$ (dashed line), the epidemic could infect from less than 0.1% to greater than 16% of the population as $I_0$ ranges from just above 0% to 3% of the population. Epidemic size was calculated using the final size equation, $Z=S_0(1-e^{-{\mathcal{R}}_0\left(Z-I_0\right)})$, where $S_0=1$. Shading indicates the cube root of epidemic size with lighter colors corresponding to smaller outbreaks.