Estimating cost-benefit of quarantine length for Covid-19 mitigation

Andreas Eilersen; Kim Sneppen

One obstacle to the widespread implementation of this strategy is difficulty of tracing contacts. Therefore, we will here implement a crude form of contact tracing where we 1) close the workplaces of people who are tested positive for the disease, 2) isolate their regular social contacts for a limited period, and 3) test people for COVID-19 just before they exit the quarantine. We will see that such a 1 step tracing and quarantine strategy (1STQ) can give a sizeable reduction in disease spread while costing fewer lost workdays than overall lockdown. Our simulations include the limitations imposed by not being able to trace the estimated 15% of infections from random public transmissions. Thus the strategy does not require sophisticated contact tracing but could be implemented based on infected people being able to recollect their recent physical encounters with friends. It should be noted that we here quarantine persons in their own households, thereby making our contact tracing strategy easier to implement in practice. In particular, family members of a quarantined person are still free to interact outside their home if they are not themselves tested positive. The drawback of such light quarantine practices is that infected persons in quarantine may still transmit the infection to their families. Fig. 3 (a,b,c) examines how increased detection efficiency systematically improves our ability to reduce the peak disease burden. This would then be a more cost efficient way to mitigate the pandemic than a complete lockdown where each person would lose several man-months. Even detecting as little as 2 % of COVID-19 infected per day (which with an average disease duration of 5 days corresponds to finding approximately 10 % of the infected) can potentially reduce the peak number of cases by 30 % . If 10 % efficiency is possible, corresponding to detecting about half of infectious cases, then peak height could be reduced by a factor 3, and with less than 12 quarantine days per person during the entire epidemic. This is illustrated in Fig. 3 (b) where peak height is reduced from 0.27 to 0.08 at 10 % testing efficiency. In supplement Figs. S4,5 one can compare this with the simpler strategy where only the infected person and their family are quarantined. The peak height is reduced, but only from 0.27 to 0.20 at 10 %/day testing efficiency.