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

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

The mitigation scenarios shown in Figs. 4-5 assume that a fixed proportion (1.25%) of all current infections are in ICU at any given time. In reality, there is a time lag between infections becoming symptomatic (compartment Iu) and become severe enough to require ICU admission. To better reflect this, we assumed that no unconfirmed cases are in ICU and a fixed proportion of confirmed cases are in ICU. The proportion of confirmed cases in ICU was set at a level that gives the same overall proportion of ICU cases in the long run. The main consequence of this change to the model is that there is longer time lag before the strong control measures start to reduce the number of new infections, which means that cases overshoot hospital capacity (Fig. 6a) . If strong control is sufficiently effective (Rc=0.75), this problem can be offset by triggering strong earlier, when ICU reaches 50% of capacity rather than 100% of capacity (Fig. 6b) . As before, if strong control is less effective than hoped for (only reducing Rc to 1.5),the mitigation strategy fails as hospital capacity is completely overwhelmed and the mortality rate doubles (Fig. 6c ).