Table 2.

Parameter estimates (and 95% confidence intervals) for COVID-19; these estimates are examples from published studies and are not based on a systematic review of the literature. WT refers to the wild-type virus. The latent period (time from exposure to infectiousness) is extremely difficult to estimate, so the incubation period (time from exposure to appearance of symptoms) is often used as a proxy. The incubation period for the Alpha variant was estimated to be $\frac{2}{3}\times (T_{\mathrm{inc}}\hspace{0.17em}\mathrm{for}\hspace{0.17em}\mathrm{WT})$ [37]. ${\mathcal{R}}_0$ is expressed in terms of the model parameters in equation (4.1). ${\mathcal{R}}_0$ for the Alpha, Delta and Omicron variants were approximated using estimates of the increase in transmissibility for each successive variant, i.e. $\text{WT}\hspace{0.17em}\stackrel{1.5\times }{⟶}\hspace{0.17em}\text{Alpha}$ [38], $\text{Alpha}\hspace{0.17em}\stackrel{1.5\times }{⟶}\hspace{0.17em}\text{Delta}$ [39–41] and $\text{Delta}\hspace{0.17em}\stackrel{4.2\times \hspace{0.17em}[2.1\times -9.1\times ]}{⟶}\hspace{0.17em}\text{Omicron}$ [42].

parameter	meaning	estimate	references
Tlat	mean latent period	3.7 [3.3–3.9] days	WT [43]
		4.0 [3.5–4.4] days	Delta [44]
Tinc	mean incubation period	6.4 [4.9–8.5] days	WT [45]
		4.2 [3.2–5.6] days	Alpha [37]
		5.8 [5.2–6.4] days	Delta [44]
		∼3 days	Omicron [46]
Tinf,m	mean infectious period for mild infections	9 [6–11] days	[47]
Tinf,s	mean infectious period for severe infections	14 [8–20] days	[48]
Tgen,m	mean generation interval for mild infections	Tlat + Tinf,m days	[49, equation (4.1)]
Tgen,s	mean generation interval for severe infections	Tlat + Tinf,s days	[49, equation (4.1)]
Timm	mean immune period	7 [6–8] months	[32,33,50]
${\mathcal{R}}_0$	basic reproduction number	3 [2.1–4.6]	WT [38]
		4.5 [3.15–6.9]	Alpha [51]
		6.75 [4.7–10.4]	Delta [39–41]
		28.4 [9.9–94.6]	Omicron [42]