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

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

Mitigation strategies allow the disease to spread then apply control to reduce the peak allowing hospitals to be less overwhelmed. In general mitigation requires an initial period of weak control to allow the epidemic to establish, then an extended period (3-4 months) of very strong control. This can be followed by periods when control measures can be loosened, but strong control needs to be re-established when cases increase towards hospital capacity. One way to approach this is alternating periods of strong control (shaded blue, Rc=0.75) and weak control (unshaded, Rc =1.75) as shown in the graphs. Fig. 4 to succeed requires control measures sufficiently strong to force Rc below 1. It remains completely unknown whether a scenario such as that shown in Fig. 4 is achievable in practice in New Zealand or any comparable country. Fig. 2 shows that the only countries that have so far succeeded in getting the effective reproduction number less than 1 are China and South Korea. In those countries, this has been achieved by extremely intensive measures, including mandatory and strictly enforced quarantine, huge amounts of resources devoted to contact tracing, electronic surveillance of citizens' movements, etc. In other countries, including those that have instigating major lockdowns such as Italy, there is as yet insufficient evidence that this has reduced Rc to 1 (Fig. 2) .