Suppression and Mitigation Strategies for Control of COVID-19 in New Zealand

Alex James; Shaun C Hendy; Michael J Plank; Nicholas Steyn

The copyright holder for this preprint . https://doi.org/10.1101/2020.03.26.20044677 doi: medRxiv preprint Mitigation. Mitigation strategies were simulated as a combination of a low level of control (case isolation and household quarantine, reducing Rc to 1.75) with periods of high control as required to try and keep the number of cases under hospital capacity. There are various ways this could be achieved. One approach is a "switching" strategy ( Fig. 4) in which strong controls are imposed when hospital capacity is close to full (shaded blue areas in Fig. 4) and relaxed when there is spare hospital capacity available. The scenario shown in Fig. 4 requires the strong control periods to reduce Rc below 1 (Rc = 0.75 during periods in strong control in Fig. 4 ). Strong control is initiated when the number of ICU cases reaches capacity, and is lifted when the number of ICU cases drops to 50% of capacity. This is comparable to the scenario tested by Ferguson et al (2020) , where weak control means Rc=1.75 (representing case isolation and household quarantine in the Ferguson et al (2020) model) and strong control means Rc=0.75 (representing the above measures plus populationwide social distancing in Ferguson et al (2020)). Periods of alternating strong/weak control are required to continue for approximately 750 days to prevent hospital capacity from being exceeded.