key: cord-0765511-101hv8uk
authors: Zhang, Lei; Tao, Yusha; Zhuang, Guihua; Fairley, Christopher K.
title: Characteristics analysis and implications on the COVID-19 reopening of Victoria, Australia
date: 2020-10-01
journal: Innovation (N Y)
DOI: 10.1016/j.xinn.2020.100049
sha: ad1c4b2d13e38c06993f094581d62d9bc3e0b9db
doc_id: 765511
cord_uid: 101hv8uk

nan

As of 24 th September 2020, the SARS-COV-2 epidemic has led to a total of 26,983 infections and 861 deaths in Australia, resulting in a significant disease burden on its health care system and disruption to its economy. The State of Victoria is the most severely affected Australian state and accounts for 74.5% of all infections and 89.7% deaths in Australia. Controlling the epidemic in Victoria is critical to the impact of the national epidemic. In response to the first outbreak of the epidemic, Victoria declared a state of emergency on 16 th March and implemented stage 2 restrictions during 25 th March and 25 th May (first lockdown) with restrictions on major events, travelling and social contacts ( Figure 1A ). In contrast, a much stricter stage 3 and subsequent stage 4 (second lockdown) restrictions were implemented in metropolitan Melbourne and regional Victoria between the 9 th July and 13 th September in response to a substantially larger second outbreak since late June. The restriction measures have been effective, and the epidemic has seen a major decline from 500-700 cases/day in early August to 30-50 cases/day in early September. In preparation for reopening the economy, the Victorian government declared a COVID-19 roadmap for reopening on 9 th September. 1 . In brief, the reopening plan for metro Melbourne requires the city to maintain a consistently declining trend of the epidemic, with the ease of restrictions in proportion to the number of the daily confirmed cases. The restrictions are less stringent for regional Victoria. The plan envisions that the complete elimination of the virus for 28 days state-wide before Victoria is allowed to return to a 'COVID normal' scenario.

We identified several key characteristics of the COVID-19 epidemic in Victoria, based on a simple bilogistic model of growth 2,3 on the cumulative number of confirmed COVID-19 cases in the state ( Figure 1B) . First, the second outbreak (estimated to saturate at 19,842 cases, Figure 1B ) is significantly greater than the first outbreak (saturate at 1,491 cases), and accounts for >90% of all reported COVID-19 cases in Victoria. Second, the duration of the second outbreak (17 th June-13 th September, 88 days) almost double that of the first outbreak (5 th March-22 nd April, 48 days). Third, the peak of the two outbreaks is approximately four months (124 days) apart, whereas the duration between the end of the first outbreak and the beginning of the second outbreak is 57 days. The large separation between the two outbreaks indicates that they are independent of each other. The 57-day duration between the two outbreaks is a period of low-level transmission, with the number of new confirmed case averaged at 8 (0-21) cases per day. Fourth, the first lockdown was initiated on 16 th March with 17 confirmed cases, whereas the second lockdown was initiated on 9 th July with a much greater number of confirmed cases (143) on that day.

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 2-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. As the number of cases continues to decline, the epidemic trend in Victoria may experience a similar period of lowtransmission during the reopening. According to the Roadmap, the threshold of daily confirmed cases needs to be less than five new cases state-wide to enable the lift of curfew, stay home requirements and intrastate travel by 26 th October (from Step 2 to Step 3 of the Roadmap). To achieve this lower threshold in the specified time period, the government will need to suppress the epidemic more quickly than in the previous low-transmission period.

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 remained closed, occasional 'seeding' due to imported cases from affected areas will J o u r n a l P r e -p r o o f be inevitable. Both China and New Zealand appeared to have largely 'eliminated' the viruses for an extensive period, yet sporadic outbreaks occurred 4, 5 . However, with early, localised and strong measures, these outbreaks were quickly controlled. In Victoria, living with the virus at a very low endemic level like some other Australian states may be an alternative, until an effective vaccine becomes available to the majority of its population 6 . However, if this approach is taken, then certain measures must continue to mitigate the risk of outbreaks in addition to compound interventions discussed above.

We recommend two measures that are potentially important for the COVID-19 reopening in Victoria. First, establishing an early epidemic alarming mechanism based on the number of daily confirmed cases. The fact that the first lockdown was implemented when the daily confirmed cases were as low as 17 cases (on 16 th March) compared with 143 cases (on 9 th July) at the beginning of the second lockdown is likely to be why a 10-time smaller in epidemic size in the first outbreak. Consistent with this, a recent study indicated that in the early stage of the epidemic, a threshold of 30 confirmed cases might represent a threshold for epidemic conversion, where the epidemic switch from a slow-growing phase to a fast-growing phase 7 . Second, persistent face mask usage inside and where social distancing is not possible should remain as a key public intervention strategy until a vaccine is available. In Victoria, compulsory face mask use in public space was not in place until 23 rd July, on which the community transmission was already close to its peak with 300-500 cases confirmed daily. This was despite the fact that more than 63 countries and regions had already adapted this policy then 8 and WHO has recommended its use based on accumulating evidence on the protective effectiveness of face mask against COVID-19 transmission 9 . Further evidence has shown that at least 70% face mask use is necessary for preventing a further outbreak if the social interaction is to return to the preepidemic level 10 . Until an effective vaccine becomes available, maintaining a high face mask use in addition to some ongoing social distancing restrictions such as COVID safe workplaces and limiting the size of family gatherings should be an effective and economic friendly strategy to minimise the risk of further major outbreaks. The number of cumulative confirmed cases was calibrated to a bi-logistic function, which was used to model biologic patterns with two growth phases. The details of the bi-logistic function have been previously documented by Meyer et al. 2, 3 The fitting of the bi-logistic function with six parameters was conducted on https://logletlab.com/. The parameters K 1 (1491) and K 2 (18,350) represent the asymptotic values that bound the function and therefore specify the level at which the epidemic saturates; t m1 (29 th March) and t m2 (31 st July) represent the midpoint of the two epidemic growth and hence the peak of the two outbreaks; ∆ (23 days) and ∆ (43 days) are the lengths of time intervals required for the epidemics to grow from 10% to 90% of the saturation level, as defined by the bi-logarithmic function; in contrast, we defined the duration of the epidemics ∆ (48 days) and ∆ (88 days) as the length of time intervals required for the epidemic to grow from 1% to 99% of the saturation level. The first lockdown period was between 16 th March and 25 th May 2020 (the State of Emergency was declared on 16 th March and Stage 2 restrictions were in place between 25 th March and 25 th May). The second lockdown period was between 9 th July and 13 th September (9 th July-20 th August, stage 3 for all Victoria; 21 st August-13 th September, stage 4 for metro Melbourne and stage 3 for regional Victoria). Compulsory face mask in public space was implemented on 23 rd July. The first step of the COVID-19 Roadmap for reopening initiated on 14 th September with most of the stage 4 restrictions remained.

State Government of Victoria. Coronavirus (COVID-19) roadmap to reopening

Bi-logistic growth

Bi-logistic model for disease dynamics caused by Mycobacterium tuberculosis in Russia

The probability of the 6-week lockdown in Victoria (commencing 9th July 2020) achieving elimination of community transmission of SARS-CoV-2

National Health Comission of the People's Republic of China,. China's risk of COVID-19 cluster infections caused by sporadic cases cannot be ignored: official

The COVID-19 vaccine development landscape

Early characteristics of the COVID-19 outbreak predict the subsequent epidemic scope

Can self-imposed prevention measures mitigate the COVID-19 epidemic?

Physical distancing, face masks, and eye protection to prevent person-to-person transmission of SARS-CoV-2 and COVID-19: a systematic review and meta-analysis

What is required to prevent a second major outbreak of SARS-CoV-2 upon lifting the quarantine of Wuhan city

The authors declare no competing interests J o u r n a l P r e -p r o o f