Figure 1
(a) Schematic algorithm of the simulation. The main steps are as follows: 1. M (= 1000) people are distributed on a one -dimensional grid having N sites (= 2000). 2. They can move freely within a window of + /− m sites (m was set to 100 when no confinement was enforced). m = 0 means that people were not allowed to move from their sites. 3. The people collocated at the same site were identified. People collocated with an infectious person were infected with a probability of T.P., and the infected people were detected with a set detection probability (D.P.) and isolated from the system (detected people cannot infect nor be infected). 4. When the detected number of infected people reached 1% of the total number of all people (1% of 1000 people in our setting), m was decreased to the values indicated in Table 1. Infected people remained infectious for a total of 15 steps: 5 steps as a presymptomatic patient, and then ten steps as a symptomatic patient. Furthermore, we assumed that the virus would disappear after 15 steps, and that the infection occurs only once. (b) Schematics of the one-dimensional grid model with four people and 21 sites. The black and white circles represent the infected and the non-infected person, respectively. The arrows illustrate the possible movement of the infected person. For m = 1, the person can move by − 1, 0, or + 1. Viral transmission occurs with a probability of T.P. when an infected person occupies the same sites as a non-infected person. The periodic boundary condition implies that a person at position 21 can move to its right and will "reappear" at position 0 (and vice versa). It is used to alleviate the effects of the boundaries. (c) Comparison of the contact probability calculated using an exact probabilistic model (supplemental), and numerically from our simulation (average over 3000 runs with N = 3, M = 21). In the initial distribution, people were regularly-spaced at positions 0, 7, and 14 on the one-dimensional grid with a periodic boundary condition (between positions 0 and 20). People were then allowed to move according to any site elements within the mobility limit set to mmax. The blue bars represent the results of the simulation, the red line those of the exact probabilistic mode, and the gray line represents the average probability of encounter for a random distribution (0.1428 for N = 3 people on a grid with M = 21 sites.
