Figure 4.

Effects of constant-strength and constant-speed interventions on the spread of a new variant with known speed r_var. (a–f) Pre-intervention (black) and post-intervention (coloured) kernel of the new variant under constant-strength (a,c,e) and constant-speed (b,d,f) interventions when the variant has shorter (a,b), equal (c,d), or longer (e,f) mean generation interval (GI) than the wild-type. Vertical lines represent the mean generation interval. (g) Pre-intervention ${\mathcal{R}}_{\mathrm{var}}$ (black) and post-intervention epidemic strength ${\mathcal{R}}_{\mathrm{post}}$ (coloured) conditional on the mean generation interval of the variant. (h) Pre-intervention $r_{\mathrm{var}}$ (black) and post-intervention epidemic speed ${\mathcal{R}}_{\mathrm{post}}$ (coloured) conditional on the mean generation interval of the variant. Epidemic strength and speed are calculated assuming $r_{\mathrm{wt}}=0\hspace{0.17em}{\mathrm{d}}^{-1}$, δ = 0.1 d⁻¹, $r_{\mathrm{var}}=0.1\hspace{0.17em}{\mathrm{d}}^{-1}$, ${\overline{G}}_{\mathrm{wt}}=5\hspace{0.17em}\mathrm{d}$ and κ = 1/5 for pre-intervention conditions. The constant-strength intervention assumes that the ratio ${\mathcal{R}}_{\mathrm{var}}/{\mathcal{R}}_{\mathrm{post}}=\theta$ remains constant. The constant-speed intervention assumes that the difference $r_{\mathrm{var}}-{\mathcal{R}}_{\mathrm{post}}=\varphi$ remains constant. Intervention strength and speed are chosen so that post-intervention strength of the new variant is 0.9 when its mean generation interval is 5 d.