Table 1. Parameters and variables for modelling viral load, test sensitivity, and expected transmissions.

Model Component	Description
V (t; V0, Vp, τp, τr)	Viral load at time t since infection. Dependence on other param- eters is described in Equation 1 and shown in Figure 1A.
V 0	Viral load at the time of infection: V0 = 3 · 10−3 based on one viral particle within ≈ 300ml of respiratory fluid [26].
Vp	Peak viral load. Adjusted to attain a specified value of R0.
τp	Time from infection to peak viral load: 1.5 to 12 days.
τr	Time from Vp to V0. Symmetry assumption (τr = τp) can be relaxed in the app.
S(v; Smax, k, LOD50)	Test sensitivity (probability that a positive sample is detected as positive) as a function of viral load, v. Dependence on other parameters described in Equation 2 and shown in Figure 1B.
Smax	Maximum test sensitivity: 99.5% for PCR, 90% for antigen tests.
k	Controls width of intermediate test sensitivity region: k = 6 for PCR and k = 1.3 for antigen tests.
LOD 50	Viral load at which test sensitivity reaches Smax/2: 102 copies/ml for PCR and 105.4 for antigen tests.
T (v; NC, h, Km, θ)	Expected transmissions per day as a function of viral load, v. Dependence on other parameters described by Equation 3 and shown in Figure 1C.
NC	Average number of close contacts per day: NC = 13 based on [28]. Appendix C explores time-dependent reduction in contacts caused by symptoms.
h	Controls width of sigmoid for transmission risk vs. viral load: h = 0.51 based on [29].
Km	Midpoint of infectiousness: Km = 8.9 · 106 copies/ml based on [29].
θ	Increased from 0.2 in Ke et al. [29] to 0.3, corresponding to a maximum per-contact transmission probability of 26%.
σ(δ, ρ)	The fraction of transmissions that would be prevented (relative to R0) if the entire population tested every ρ days and received test results after δ delay.
δ	Time delay before receiving a test result. 0 for antigen tests and 2+ hours for PCR.
ρ	Time between tests.
γ	Fraction of the population that adheres to regular testing.
β	Fraction reduction in transmissions after a person who tests regularly learns they are positive.
R 0	Expected transmissions per infected person with no population immunity or disease-control measures.
Re	Expected transmissions per infected person given interventions, with no population immunity.