Optimizing the COVID-19 Intervention Policy in Scotland and the Case for Testing and Tracing

Grothey, A.; McKinnon, K. I. M.

Unlike other European countries the UK has abandoned widespread testing and tracing of known SARS-CoV-2 carriers in mid-March. The reason given was that the pandemic was out of control and with wide community based spread it would not be possible to contain it by tracing any longer. Like other countries the UK has since relied on a lockdown as the main measure to contain the virus (or more precisely the reproduction number R at significant economic and social cost. It is clear that this level of lockdown cannot be sustained until a vaccine is available, yet it is not clear what an exit strategy would look like that avoids the danger of a second (or subsequent waves). In this paper we argue that, when used within a portfolio of intervention strategies, widespread testing and tracing leads to significant cost savings compared to using lockdown measures alone. While the effect is most pronounced if a large proportion of the infectious population can be identified and their contacts traced, under reasonable assumptions there are still significant savings even if the fraction of infectious people found by tracing is small. We also present a policy optimization model that finds, for given assumptions on the disease parameters, the best intervention strategy to contain the virus by varying the degree of tracing and lockdown measure (and vaccination once that option is available) over time. We run the model on data fitted to the published COVID-19 outbreak figures for Scotland. The model suggests an intervention strategy that keeps the number of COVID-19 deaths low using a combination of tracing and lockdown. This strategy would only require lockdown measures equivalent to a reduction of R to about 1.8--2.0 if lockdown was used alone, at acceptable economic cost, while the model finds no such strategy without tracing enabled.