Feasibility of controlling 2019-nCoV outbreaks by isolation of cases and contacts

Joel Hellewell; Sam Abbott; Amy Gimma; Nikos I Bosse; Christopher I Jarvis; Timothy W Russell; James D Munday; Adam J Kucharski; W John Edmunds; CMMID nCoV working group; Sebastian Funk; Rosalind M Eggo

We implemented a branching process model in which the number of potential secondary cases produced by each individual (the 'infector') is drawn from a negative binomial distribution with a mean equal to the reproduction number, and heterogeneity in the number of new infections produced by each individual 6, 15, [18] [19] [20] . Each potential new infection was assigned a time of infection drawn from the serial interval distribution. Secondary cases were only created if the infector had not been isolated by the time of infection. In the example in Figure 1 , person A can potentially produce three secondary infections (because three is drawn from the negative binomial distribution), but only two transmissions occur before the case was isolated. Thus, a reduced delay from onset to isolation reduced the average number of secondary cases in the model. Figure 1 : Example of the simulated process that starts with person A being infected. After an incubation period (blue) person A shows symptoms and is isolated at a time drawn from the delay distribution (green) ( Table 1) . A draw from the negative binomial distribution with mean R0 and distribution parameter determines how many people person A potentially infects. For each of those, a serial interval is drawn (orange). Two of these exposures occur before the time that person A is isolated. With probability ρ, each contact is traced, with probability 1-ρ they are missed by contact tracing. Person B is successfully traced, which means that they will be isolated without a delay when they develop symptoms. hey could, however, still infect others before they are isolated. Person C is missed by contact tracing. This means that they are only detected if and when symptomatic, and are isolated after a delay from symptom onset. Because person C was not traced they infected two more people (E and F) in addition to person D than if they had been isolated at symptom onset. A version with asymptomatic transmission is given in Figure S8 .