How effective have COVID-19 mitigation strategies been in Australia's second wave?

Researchers have modeled the effect of the different types of social distancing implemented in Australia's greater Melbourne area in response to the county's second wave of coronavirus disease 2019 (COVID-19) cases. They found implementing stricter lockdowns in the beginning before the rapid rise in cases works best. The team's findings have been made available on the preprint server, medRxiv*.

The ongoing COVID-19 pandemic, caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has resulted in several mitigation strategies aimed at curbing the pathogen's spread. During the initial phase of the pandemic, one strategy used in many parts of the world was the instigation of stringent lockdown or stay-at-home orders followed by continued social distancing measures after lockdown restrictions had been eased. However, the challenge for governments and policymakers worldwide has been when exactly to implement such strategies and how to react rapidly to developing outbreaks.

Melbourne, Australia - Jul 24, 2020: Statue in Port Melbourne with face mask on put on by pranksters, Melbourne VIC, Australia. Image Credit: Alex Cimbal / Shutterstock
Melbourne, Australia - Jul 24, 2020: Statue in Port Melbourne with face-mask on put on by pranksters, Melbourne VIC, Australia. Image Credit: Alex Cimbal / Shutterstock

In Australia, the response to the initial outbreak was largely contained by implementing such strategies. This resulted in low levels of virus transmission. Almost all cases were from overseas travelers who had to undergo a mandatory 14-day hotel quarantine. Some states also closed their borders.

The low number of cases and deaths allowed for the easing of lockdown and social distancing measures, starting from May 2020. The total deaths remained around 100 up to 6 May 2020 and did not change for the next two months.

However, by late May, there was a breakdown in the quarantine regulations in Melbourne, leading to many large-scale and family gatherings, both of which caused the number of cases to dramatically increase from June 2020 onwards.

Since this second wave of the pandemic was restricted geographically to greater Melbourne, and was "self-contained," it provided an opportunity for researchers to evaluate the interventions used and how the timing of their activation affected the outcome.

Modeling the effect of social distancing strategies

Researchers from the University of Western Australia developed a model that used the demographics and people movement patterns of individual persons within an Australian city and SARS-CoV-2 virus transmission data from Wuhan, China, before any interventions were in place. This was then used to analyze the effect of non-pharmaceutical interventions (NPIs) like lockdowns and social distancing measures. The researchers used Newcastle, a city in New South Wales, as a model and applied that Melbourne.

Social distancing measures were applied in stages, with increasing stringency. When schools closed on 26 June 2020, it reflected 'Stage 2' measures. 'Stage 3' was activated on 2 July 2020, and as cases continued to increase, 'Stage 4' measures were implemented on 3 August 2020, which required people to stay at home unless they were in approved occupations, they needed healthcare, or needed to shop for essentials. The authors ran simulations to predict the effect of the different stages on the number of positive cases.

They found that if 'Stage 4' lockdown was implemented immediately after 'Stage 2', rather than the stepped response that followed, the number of cases could have been significantly reduced – by almost 50%, they speculate, if this was implemented in the latter half of June 2020. If, however, 'Stage 4' lockdown had not been imposed at all, the number of positive cases would have continued for about a year. In general, the reduction in the total number of cases was almost linear with the strength of the social distancing measures adopted. Activating 'Stage 3' measures slightly earlier did not result in a significant decrease in virus transmission.

Timing social interventions critical

Thus, the researchers found, the best strategy is to move directly to stricter lockdown measures rather than a graded approach. It is important to "catch" increasing transmission rates before they become widespread.

Furthermore, the results indicate how critical the timing of the response is. Early and rapid implementation of social distancing strategies will help reduce the number of cases, whereas a slow response to exponential growth in the number of cases can result in a rapid spread among the population.

The analyses indicated that the Australian Government's decision to implement 'Stage 4' lockdown suppressed transmission and shortened the second wave's duration. Suppressing rapid transmission quickly allows the easing of social distancing measures, putting into place efficient testing and tracking of cases, and earlier resumption of economic activity.

"Given that case data always lags the date of virus transmission, our findings indicate that activation of early lockdown is possibly the only feasible strategy to adopt," write the authors.

However, the authors note that their analysis may not be applicable to other countries where there is community transmission. The strategy worked in Australia because there was no community transmission before the second wave and cases were restricted to the greater Melbourne area.

Other countries that are in different situations with virus transmission may need different strategies to contain the spread. Modeling studies for the USA and Paris, for example, highlight the need for robust testing, contact tracing, and the isolation of COVID-19 positive persons.

*Important Notice

medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Journal reference:
Lakshmi Supriya

Written by

Lakshmi Supriya

Lakshmi Supriya got her BSc in Industrial Chemistry from IIT Kharagpur (India) and a Ph.D. in Polymer Science and Engineering from Virginia Tech (USA).

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