Sydney COVID-19 outbreak extended significantly by minor non-compliance, modelling shows

New research shows that under the current settings, Sydney could be in COVID-19 lockdown for weeks and that even a small drop in compliance could extend it significantly.

• Modelling from the University of Sydney showed 70 per cent compliance would see the outbreak lasting two months
• A business advocacy group has pressured the NSW Government for clear definitions of essential workers
• The modelling has been published online but not yet subjected to a rigorous peer-review process

The University of Sydney has used complex modelling to forecast the city's outbreak, factoring in the high infectiousness of the Delta variant, school closures, isolation of positive cases and home quarantine of contacts.

It found, using data available up until July 13, that if 80 per cent of Sydneysiders complied with social distancing measures it would take a month for cases to reduce from the peak to below 10.

That is two weeks later than the July 30 deadline currently in place, assuming the peak of this outbreak is the 112 locally acquired cases announced on Monday. 

However, if compliance fell to 70 per cent, it would take more than two months to bring the outbreak under control.

Study lead Mikhail Prokopenko said 80 per cent compliance relied on four out of five Sydneysiders drastically reducing their contact with others to 10 per cent of what they would normally have.

"For example, this would mean reducing your shopping frequency or duration to just one out of 10 typical trips or hours. So, if someone spent 10 hours a week doing the shopping, now it needs to reduce to just one hour of shopping a week," he said.

He estimated only 40 per cent were complying with stay-at-home measures.

"Our modelling indicates that the level of social distancing currently attained in Sydney is inadequate for outbreak control," Professor Prokopenko said.

He said while the case numbers in the epidemic corresponded to 40 per cent compliance in the model, it did not take account of real-world information such as mobility data.

If Sydney was to achieve 80 per cent compliance, some services currently regarded as essential would need to be included in the lockdown restrictions, Professor Prokopenko said.

NSW Premier Gladys Berejiklian has been under pressure to define "essential workers" who are permitted to leave the house each day, but has so far refused to do so.

She defended the current restrictions in place yesterday, saying the state was "starting to see the results" come through.

The model, which uses census data about the Sydney population, assumes that workers delivering essential services account for 19 per cent of the population, when functions like healthcare and social assistance, postal and utilities like water and electricity were included.

If construction, manufacturing, and retail and wholesale trade were included in essential services, the proportion of the population involved went up to 33 per cent.

Fazila Farhad, director of the Liverpool Chamber of Commerce in south-west Sydney, said the lack of definition of an essential service meant all kinds of businesses had continued trading.

"A lot of businesses shut down and then some of them opened back again because … it's like day-to-day survival," she said.

Ms Farhad said police presence had been impacting foot traffic in the south west, where police launched a high-visibility operation last week to crack down on non-compliance.

The uncertainty for businesses, she said, could be mitigated through the introduction of more guidelines.

"Otherwise, businesses are going to start closing down — especially small businesses."

The modelling was created by the Centre for Complex Systems and the Sydney Institute for Infectious Diseases at Sydney University. It has been published online but has not yet been through a rigorous peer-review process.

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