Sharper restrictions now might save Sydney from more COVID cases

Modelling from the Burnet Institute suggests that Sydney is in for a long COVID-19 haul if stricter lockdown measures aren’t implemented.

The Institute’s modelling shows that while the lockdown in Sydney is preventing catastrophe, a significant decline in new COVID-19 cases is only likely with even tighter restrictions – more like the Victorian Stage 4 restrictions that were implemented a year ago to control their second wave.

The modelling has been done using the COVASIM mathematical model developed by the Burnet Institute and the Institute for Disease Modelling in the US, which takes data from a range of countries to predict COVID spread and prevalence.

It is based on this week’s case data combined with the restrictions introduced on July 9, and has been calibrated against data from Victoria’s second wave. It has not been peer-reviewed, but the COVASIM model has been the subject of several peer-reviewed publications, and it takes the increased infectiousness of the Delta variant into account, as well as contact tracing and vaccine coverage as of 1 July 2021.

“There is little doubt that whilst the current strategy of NSW Health has impacted on the course of the epidemic, including their stay-at-home measures, mask policy and trace and track interventions, our modelling indicates more is needed to stop this infectious Delta outbreak,” says Professor Margaret Hellard, deputy director of the Burnet Institute.

“NSW’s current restrictions are approximately equivalent to Victoria’s ‘Stage 3 plus masks’ restrictions, so the good news is they still have ‘room to move’ in tightening the public health response. Contact tracing has been beneficial and remains critical.”

The model suggests that if the current restrictions are kept in place, daily case numbers won’t rise much more, but they’re also unlikely to fall below ~40 cases per day for well over the next two months – an ‘unacceptable amount of time’, according to the researchers.

However, if rules comparable to Victoria’s stage 4 restrictions were brought in – including closing non-essential retail, tightening open businesses, and overnight curfews – there would be a much sharper decline in new cases per day.

The effectiveness of these restrictions relies on the community’s willingness to follow them.

“Community engagement should be enhanced and form the backbone of adherence measures,” says Hellard.

“Where necessary individuals and communities should be supported to help them comply and follow the restrictions.”

It’s difficult to tell how fast the state could get to zero local transmission with Stage 4, but the model estimates very low new case numbers per day (<5) within six weeks.

The researchers also considered the impact of reducing restrictions at this point. Even with optimistic vaccination uptake (300,000 doses per week, with a vaccine that was 80% effective, eventually covering 70% of the total population), NSW could expect 3000-5000 deaths in this scenario.

That’s 12 times as many deaths as occurred from influenza in 2017 (one of our worst influenza years on record). The researchers point out that “a subsequent long lockdown would almost certainly be unavoidable”.

More information on the predictions from the model are available from the Burnet Institute’s website. You can also download the COVASIM model as an Excel file yourself, if you’re interested in testing different modelling scenarios.

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