Table 1.

Parameter values.

quantity	description	source
fixed
Npop = 523 000	NL population size	estimated as 519 716 in 2016 [10]
π = 0.15	proportion of infections that are asymptomatic	estimated as 17% in Byambasuren et al. [11]. Known to take a wide range of values [12,13].
ηS = 0.25	proportion reduction in infectivity for asymptomatic infections relative to clinical infections	[9]
ciso = 0.5	proportion reduction in infectivity for individuals with clinical infections due to self-isolation	[9]
R0 = 2.4	the pre-pandemic basic reproduction number. This is the number of secondary infections generated by an individual with a pre-clinical infection over their entire infectivity period, when all individuals in the population are susceptible. For our model, the definition of R0 supposes that the level of infectivity corresponding to a pre-clinical infection is retained for the entire duration of the infectivity period (see the electronic supplementary material, equation S1). Note that a change in R0 relative to its pre-pandemic level is equal to the same change in the contact rate if all other contributors to R0 (i.e. the recovery rate and the probability of infection given a contact) are assumed unchanged	Assumed
c1 = 30%	contact rate after 18 March 2020, expressed as a percentage of the pre-pandemic contact rate	Estimated from NL COVID-19 case data (figure 2)
c2 in [40%, 70%]	contact rate after 4 May 2020, expressed as a percentage of the pre-pandemic contact rate	Range considered
sampled
W(2.83,5.67)	infectivity, which depends on the number of days since the date of infection (Weibull-distributed)	[14]
s ∼ Γ(6.1, 1.7)	the time from date of infection to self-isolation (gamma-distributed)	[7]. Note that s ≈ T1 + T2, where T1 and T2 appear in [7].
z1 ∼ POIS(0.008)	the number of imported infected individuals per month that fail to self-isolate when travel restrictions are in place after 4 May 2020 (Poisson-distributed). The mean value is 0.24 infected travellers per month that fail to self-isolate.	Fit to NL COVID-19 case data when c2 ≤ 60% (figure 2)
z2 ∼ POIS(0.1)	the number of imported infected individuals per month that fail to self-isolate when there are no travel restrictions after 4 May 2020 (Poisson-distributed). The mean value is three infected travellers per month that fail to self-isolate.	the mean importation rate is reduced by 92% when travel restrictions are in place since z1 = (1 − 0.92)z2. Therefore, the z2 value is consistent with data reporting a 92.2% decrease in the number of passengers arriving at St. John's airport (NL) in June 2020 relative to June 2019 [15]. Equivalently, this assumption can be stated as that without travel restrictions the importation rate is 12.5 times greater (=0.1/0.008).