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 addition, each case had an independent probability of being subclinical, and was therefore not detected either by self-report or contact tracing. New secondary cases caused by a subclinical case were missed by contact tracing and could only be isolated on the basis of symptoms. The model included isolation of symptomatic individuals only-ie, no quarantine, so isolation could not prevent transmission before symptom onset. In the model, subclinical cases were never isolated, whereas symptomatic cases might transmit before symptoms appear, but were eventually isolated. Quarantining contacts of cases (ie, individuals who are not yet symptomatic, and might not be infected) requires a considerable investment in public health resources, and has not been widely implemented for all contacts of cases. 3 However, some countries have adopted a quarantine or self-quarantine policy for airline travellers who have returned from countries with confirmed COVID-19 transmission. 23