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

We determined conditions in which case isolation, contact tracing, and preventing transmission by contacts who are infected would be sufficient to control a new COVID-19 outbreak in the absence of other control measures. We found that in some plausible scenarios, case isolation alone would be unlikely to control transmission within 3 months. Case isolation was more effective when there was little transmission before symptom onset and when the delay from symptom onset to isolation was short. Preventing transmission by tracing and isolating a larger proportion of contacts, thereby decreasing the effective reproduction number, improved the number of scenarios in which control was likely to be achieved. However, these outbreaks required a large number of cases to be contact traced and isolated each week, which is of concern when assessing the feasibility of this strategy. Subclinical infection markedly decreased the probability of controlling outbreaks within 3 months.