Modelling indicates more Sydney-siders should keep their distance to control COVID-19

By Melissa Coade

Friday July 16, 2021

Social distancing compliance must double to 80%; at a rate of 70%, the modelling determined, positive COVID-19 cases would decrease after two months.
Social distancing compliance must double to 80%; at a rate of 70%, the modelling determined, positive COVID-19 cases would decrease after two months. (Iryna/Adobe)

New modelling has shown that Sydney’s COVID-19 Delta outbreak is not being adequately controlled by the current level of social distancing (approximately 40% of compliance) at play. 

According to the data, to get on top of the outbreak within a month, social interactions such as shopping must decrease to a tenth of ‘normal social interactions’. 

Social distancing compliance must double to 80% to see a reduction of cases after one month. At a rate of 70% compliance, the modelling determined positive COVID-19 cases would decrease after two months.

The data was produced by the University of Sydney’s Centre for Complex Systems by analysing information about Sydney’s current COVID-19 situation until 13 July.

Centre director Professor Mikhail Prokopenko said social distancing was an effective way of stemming the spread of the SARS-CoV-2 Delta variant in Sydney.

“The outbreak is of major concern as the Delta variant is estimated to have twice the reproductive number of previous variants that circulated in Australia in 2020, which is also worsened by low levels of acquired immunity in the population,” Prokopenko said.

On Friday the NSW government announced 97 new COVID-19 cases had been recorded, 29 of whom were in the community while infectious. A total of 75 COVID-19 patients have been admitted to hospital in NSW and 18 of those are in intensive care. 

In practical terms, the social distance needed to be effective would mean reducing the number of times a person goes shopping and how long they spend at the shops, Prokopenko added. 

“Compliance with 80% social distancing would mean that 4 out of 5 people must drastically reduce their contact with others to just 10% of what they normally do.

“For example, this would mean reducing your shopping frequency or duration to just 1 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. 

Prokopenko suggested that other ways to improve social distancing compliance included avoiding in-person chats with neighbours or other activities that involved being around people who live in different households.

He also noted that the NSW government would have to limit the types of jobs it deemed to be ‘essential work’ to realise the 80% social distancing compliance target. 

“Crucially, 80% of social distancing also means that many services currently deemed essential would need to be included under the lockdown restrictions,” Prokopenko said. 

The modelling – which has not been peer-reviewed – was generated using the University of Sydney’s pre-print server arXiv. The re-calibrated agent-based model was used to explore ‘a feasible range of non-pharmaceutical interventions, in terms of both mitigation (case isolation, home quarantine) and suppression (school closures, social distancing)’.


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