Table 1. Model population definitions and initial values denoted with subscript 0 for each state variable.

Here we present definitions for the population groups represented by each compartment as well as their initial values. The initial value of the S and I_S populations vary by country, as shown in Table 2. We take the initial value of the I_A population to be the same as the initial value of symptomatic individuals as a conservative estimate. The initial value of the E population is computed by assuming that all initially-infected people (I_A0 + I_S0) have exposed the virus to approximately ${\mathcal{R}}_0\left(\approx 2.5\right)$ other people.

Symbols	Initial Values	Units	Definitions	Sources
S0	Varies by country	people	Susceptible individuals	Vary
E0	${\mathcal{R}}_0\cdot \left(I_{A0}+I_{S0}\right)$	people	Exposed individuals	Deduced
IA0	IS0	people	Asymptomatic individuals	Deduced
IS0	Varies	people	Symptomatic individuals	Deduced
Rec0	0	people	Recovered individuals	Deduced
W0	1%	unitless	% of viruses in environment	Deduced