Fig. 1.

Estimates of the ${\mathcal{R}}_0$ of SARS-CoV-2 vary substantially between locations (Binny et al., 2020, Chen et al., 2020, Choi and Ki, 2020, Deb and Majumdar, 2020, Giordano et al., 2020, Johndrow et al., 2020, Ke et al., 2020, Korolev, 2021, Lewnard et al., 2020, Li et al., 2020b, Majumder and Mandl, 2020, Mizumoto et al., 2020, Peirlinck et al., 2020, Pitzer et al., 2020, Ranjan, 2020, Read et al., 2020, Riou and Althaus, 2020, Sanche et al., 2020, Senapati et al., 2020, Shim et al., 2020, Singh and Adhikari, 2020, Tang et al., 2020, Wu et al., 2020, Xiao et al., 2020, Yuan et al., 2020, Zhao et al., 2020). Each point represents a literature-compiled average ${\mathcal{R}}_0$ estimate for a different geographic area (sample size noted alongside means, error bars show plus or minus 1 standard error). For individual studies that provided multiple estimates for a single geographic area, the median estimate was used to avoid pseudo-replication. An analysis (not shown) confirmed that ${\mathcal{R}}_0$ estimation method (transmission model, exponential growth model, or stochastic simulation method) did not drive the pattern of variation in ${\mathcal{R}}_0$ by location. Recent meta-analyses of ${\mathcal{R}}_0$ values for SARS-CoV-2 consider the effects of estimation methods in more detail (Alimohamadi et al., 2020, Barber et al., 2020).