Feasibility of controlling COVID-19 outbreaks by isolation of cases and contacts

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

After an incubation period, person A shows symptoms and is isolated at a time drawn from the delay distribution (table) . A draw from the negative binomial distribution with mean reproduction number (R 0 ) and distribution parameter determines how many people person A potentially infects. For each of those, a serial interval is drawn. Two of these exposures occur before the time person A is isolated. Each contact is traced with probability ρ, with probability 1-ρ they are missed by contact tracing. Person B is successfully traced, which means that they will be isolated without delay when they develop symptoms. They 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 subclinical transmission is given in the appendix (p 12). set to the incubation period for that case, an SD of 2, and a skew parameter chosen such that a set proportion of serial intervals were shorter than the incubation period (meaning that a set proportion of transmission happened before symptom onset; figure 2 ). This sampling approach ensured that the serial interval and incubation period for each case was correlated, and prevented biologically implausible scenarios where a case could develop symptoms soon after exposure, but not become infectious until very late after exposure and vice versa.