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

There are many estimates of the reproduction number for the early phase of the COVID-19 outbreak The incubation distribution estimate fitted to data from the Wuhan outbreak by Backer and colleagues. 22 (C) An example of the method used to sample the serial interval for a case that has an incubation period of 5 days. Each case has an incubation period drawn from the distribution in (B), their serial interval is then drawn from a skewed normal distribution with the mean set to the incubation period of the case. In (C), the incubation period was 5 days. The skew parameter of the skewed normal distribution controls the proportion of transmission that occurs before symptom onset; the three scenarios explored are less than 1%, 15%, and 30% of transmission before onset. in Wuhan, China, 15, 17, 18, 21, [24] [25] [26] [27] [28] and therefore we used the values 1·5, 2·5, and 3·5, which span most of the range of current estimates (table) . We used the secondary case distribution from the 2003 SARS outbreak, 19 and tested the effect of lower heterogeneity in the number of secondary cases 29 as a sensitivity analysis (appendix pp 2-5). We calculated the effective reproduction number (R eff ) of the simulation as the average number of secondary cases produced by each infected person in the presence of isolation and contact tracing. We present results in relation to the baseline scenario of R 0 of 2·5, 21 20 initial cases, a short delay to isolation, 20 15% of transmission before symptom onset, 30 and 0% subclinical infection. 31 Values of the natural history represent the current best understanding of COVID-19 transmission, and we used 20 index cases and a short delay to isolation to represent a relatively large influx into a setting of high awareness of possible infection. 23