Table 2.

The estimated values of ${\mathcal{R}}_0$ for COVID-19 in prior studies.

${\mathcal{R}}_0$	Country	Reference
5.25	Brazil	Crokidakis (2020a, b)
3.28 (average of estimations in 12 studies)	China	Liu et al. (2020)
$4.50\pm 1.44$	European Union	Linka et al. (2020)
4.5	Global (across many nations)	Katul et al. (2020)
2.56	India	Rai et al. (2020)
2.7 (95%CI, 2.1–3.4)	Iran	Khosravi et al. (2020)
2.6 (95%CI, 2.3–2.9) or 3.3 (95%CI, 3.0–3.6)	Italy	Zhuang et al. (2020)
1.954 (95%CI, 1.851–2.025)	Japan	Chen et al. (2020)
1.49 (95%CI, 1.30–1.70)	Japan	Kobayashi et al. (2020)
2.86 (95%CI, 2.73–2.97)	Japan	Kurita et al. (2020)
2.50 (95%CI, 2.43–2.55)	Japan	Sugishita et al. (2020)
2.6 (95%CI, 2.3–2.9) or 3.2 (95%CI, 2.9–3.5)	Republic of Korea	Zhuang et al. (2020)
4.234 (95%CI, 3.764–4.7)	Russia	Nabi (2020)
4.02 (95%CI, 3.69–5.15)	USA	Gunzler (2020)