Effectiveness of Isolation and Contact Tracing for Containment and Slowing Down a COVID-19 Epidemic: A Modelling Study

Background: Novel coronavirus (SARS-CoV-2) is extending its range of transmission in all parts of the world, with substantial variation in rates of transmission and severity of associated disease. Methods: We evaluated whether and under which conditions it is possible to control and slow down a COVID-19 epidemic in the early stages by isolation and contact tracing. We used a stochastic transmission model in which every person generates novel infections according to a probability distribution that is affected by the incubation period distribution (time from infection to symptoms), distribution of the latent period (time from infection to a person becoming infectious), and overall transmissibility. The model distinguishes between close contacts (e.g., within a household) and other contacts in the population. Findings: The analyses showed that transmissibility and the duration of the latent period relative to the duration of incubation period have strong impact on the controllability of the disease. Delays in diagnosis of cases and proportion of asymptomatic cases are key factors for containment and slowing down the epidemic. Interpretation: Isolation and contact tracing can be an effective means to control early epidemics, but only if transmissibility as measured by R0 is in the lower ranges of reported values. Timeliness as well as completeness of tracing and diagnosis of cases are paramount to achieve containment and effective slowing down of the epidemic growth rate. Funding Statement: This research was funded by the Dutch Ministry of Health, Welfare and Sport and by ZonMw project number 91216062. Declaration of Interests: The authors declare no competing interests.