Effectiveness of isolation and contact tracing for containment and slowing down a COVID-19 epidemic: a modelling study

Mirjam E Kretzschmar; Ganna Rozhnova; Michiel E van Boven

owns are sufficient to 83 stop the SARS-CoV-2 outbreak (https://www.reuters.com/article/us-health-coronavirus-84 who-ryan/lockdowns-not-enough-to-defeat-coronavirus-whos-ryan-idUSKBN2190FM). 85 Possibly, additional measures are needed, for example active tracing of contacts in 86 combination with isolation of infected contacts. Also, such measures will be important in the To what extent local containment or local slowing down of an epidemic by isolation and 92 contact tracing is successful depends on the fraction of infections that remain asymptomatic 93 or have mild disease, and on the infectiousness before the onset of symptoms [4, 5] . It is 94 known that a high probability of asymptomatic infection, a high proportion of transmission 95 occurring before the onset of symptoms, a long delay between case finding and isolation, 96 and high overall transmissibility all factor in negatively in the likelihood that an outbreak can 97 7 be contained [6] [7] [8] [9] . For SARS-CoV-2, evidence indicates that a high fraction of infected 98 persons is infectious before they show symptoms (up to 50%), that a substantial fraction of 99 infections may be asymptomatic or show only mild symptoms (up to 80%), and that the We focus on conditions that make containment of an early epidemic possible, but also on 114 the impact of isolation and contact tracing when containment is not possible, or in an exit 115 phase from social distancing. In a population with social distancing in place, we investigate 116 what the additional impact of isolation and contact tracing can be for reaching containment 117 or slowing down the spread. We report effective reproduction number, the (exponential) 118 rate of increase, and the doubling time of the epidemic for scenarios with various 119 combinations of interventions. Considering that the capacity of healthcare systems is 120 . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.