Can the app contain the spread? An agent-based model of COVID-19 and the effectiveness of smartphone-based contact tracing.

A contact-tracing strategy has been deemed necessary to contain the spread of COVID-19 following the relaxation of lockdown measures. Using an agent-based model, we explore one of the technology-based strategies proposed, a contact-tracing smartphone app. The model simulates the spread of COVID-19 in a population of agents on an urban scale. Agents are heterogeneous in their characteristics and are linked in a multi-layered network representing the social structure - including households, friendships, employment and schools. We explore the interplay of various adoption rates of the contact-tracing app, different levels of testing capacity, and behavioural factors, to assess the ability of this track-and-trace strategy to mitigate the epidemic. Results suggest that the app can contribute substantially to the reduction of infections in the population, although complete suppression of the virus is unlikely to be achieved. The model also shows that, while adopting the app is beneficial for epidemic control in most cases, a high adoption rate is likely to generate an extensive increase in the demand for testing, which, if not met with adequate supply, may render the app counterproductive. This points to the crucial role of an efficient testing policy and the necessity to upscale testing capacity.