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

In scenarios in which the reproduction number was 2·5, 15% of transmission occurred before symptom onset, and there was a short delay to isolation, at least 80% of infected contacts needed to be traced and isolated to give a probability of control of 90% or more. This scenario echoes other suggestions that highly effective contact tracing will be necessary to control outbreaks in other countries. 16 In scenarios in which the delay from onset to isolation was long, similar to the delays in the early phase of the outbreak in Wuhan, the same contact tracing success of 80% achieved a probability of containing an outbreak of less than 40%. Higher presymptomatic transmission decreases the probability that the outbreaks were controlled, under all reproduction numbers and isolation delay distributions tested.