How to keep COVID waves small

Monash study reveals Stage 4 started too late to control COVID-19 community transmission, and recommends an early warning system and national mandatory mask wearing.

A Monash University researcher who studied Victoria’s first and second waves of COVID-19 infections found the Stage 3 restrictions and mandatory mask wearing were introduced too late and led to the prolonged Stage 4 lockdowns.

The second lockdown was introduced on 9 July when the state recorded 143 cases in one day, whereas the first lockdown was initiated on 16 March with just 17 confirmed cases.

Associate Professor Lei Zhang, Head of the Artificial Intelligence and Modelling in Epidemiology Program at Monash University’s Melbourne Sexual Health Centre, is publishing his results in The Innovation, a Cell Press journal.

The data reveal the second wave – where numbers of active cases peaked at over 700 a day – has been twice as long and 10 times as big as the first wave. “The fact that we have such a long and protracted second wave is evidence that the decision to enter Stage 3 restrictions was taken too late,” he said.

“Essentially we entered Stage 3 at 150 cases a day, which was twice the peak of the first wave during the first lockdown.”

The paper adds that the delay in introducing mandatory mask wearing also has resulted in a long second lockdown, and that NSW, which has continued to record double-digit numbers of new cases daily, should promptly introduce mandatory mask wearing to prevent a Victorian-like second wave.

The large separation between the two waves indicates, according to the study, that the two are independent, which has been borne out by genomic data linking the second wave almost entirely to the isolation hotels.

Previous published research by Associate Professor Zhang has shown that once the cumulative active case figures go above 30 then “it is very hard to control.”

He added that Victoria’s track and trace system must be robust enough – for the foreseeable future – to ensure that active cases remain under 30, to prevent a third wave.

In response to the first outbreak of the epidemic, Victoria declared a state of emergency on 16 March and implemented stage 2 restrictions during 25 March and 25 May (first lockdown) with restrictions on major events, travelling and social contacts.

Much stricter stage 3 and subsequent stage 4 (second lockdown) restrictions were implemented in metropolitan Melbourne and regional Victoria between 9 July and 13 September in response to a substantially larger second outbreak since late June.

According to Associate Professor Zhang, the restriction measures were effective, with major decline from 500-700 cases/day in early August to 30-50 cases/day in early September.

According to the Roadmap outlined on 9 September, the reopening plan for metropolitan Melbourne requires the city to maintain a consistently declining trend of the epidemic, with the easing of restrictions in proportion to the number of the daily confirmed cases.

The plan envisions the complete elimination of the virus for 28 days state-wide before Victoria is allowed to return to a ‘COVID normal’ scenario.

According to Associate Professor Zhang, achieving complete elimination of COVID-19 in Victoria, as recommended in the Roadmap, may face challenges if the pattern for the later part of the second outbreaks follows what happened with the first.

“Our analysis demonstrates a period of nearly two-month low transmission period following the first outbreak in Victoria. This persistent low-level transmission may represent a scenario where limited community transmission was contained by a compound of interventions including rapid screening, contact tracing, isolation of infected individuals and those in close contact. This balance was later broken when transmission entered a population, and workplaces and large families gatherings had led to a large surge in positive cases that overwhelmed the compound of interventions,” he said.

As the number of cases continues to decline, the data indicate that  there may be a period of low transmission during the reopening. According to the Roadmap, this low transmission will have to remain at less than five new cases state-wide to enable the lift of curfew, stay-at-home requirements and intrastate travel.

According to Associate Professor Zhang, to achieve this lower threshold in the specified time period, the government will need to suppress the epidemic more quickly and harder than in the previous low-transmission period.

In addition, complete elimination in Victoria would also necessarily require other Australian states to adopt the same target. “Unless all Australian states are completely free of the virus or the country’s state and national borders remain closed, there will be occasional ‘seeding’ due to imported cases from affected areas,” he said.

Both China and New Zealand appeared to have largely ‘eliminated’ the viruses for an extensive period, yet sporadic outbreaks have happened. However, despite the many differences between the two countries, with similarly early, localised and strong measures, these outbreaks were quickly controlled.

The paper recommends two measures that are potentially important for the COVID-19 reopening in Victoria.

  • Establish an early epidemic alarming mechanism based on the number of daily confirmed cases.
  • Routine face mask usage in public space and where social distancing is not possible should remain as a key public intervention strategy until a vaccine is available.

“We really need to consider mandatory mask wearing in NSW if we are to keep the national numbers down,” Associate Professor Zhang said.

Zhang, L., Tao, Y., Zhuang, G., Fairley, C.K, Characteristics analysis and implications on the COVID-19 reopening of Victoria, Australia, The Innovation (2020), doi: https:// doi.org/10.1016/j.xinn.2020.100049.

Zhang, L., Tao, Y., Zhuang, G., Fairley, C.K, Characteristics analysis and implications on the COVID-19 reopening of Victoria, Australia, The Innovation (2020), doi: https:// doi.org/10.1016/j.xinn.2020.100049.

20 October Herald Sun, "Earlier action would have cut Victoria's lockdown in half" by Grant MacArthur