Social distancing up but still inadequate to control outbreak

University of Sydney model released today finds if even 40 percent of the Greater Sydney population is vaccinated by mid-September, a stricter lockdown must continue until then.

COVID-19 modeller and Director of the University of Sydney’s Centre for Complex Systems Professor Mikhail Prokopenko, Dr Sheryl Chang, Dr Oliver Cliff and Dr Cameron Zachreson have today released updated modelling on pre-print server arXiv that shows Sydney’s current level of social distancing is still inadequate for outbreak control.

Fig 2.a Levels of social distancing needed to see a drop off in case numbers over time. Credit: Professor Mikhail Prokopenko.

The modelling analysed the period between 16-25 July 2021, finding that although the actual incidence growth has reduced from 10 to 3.7 percent, social distancing currently sits at around 60 percent, which is still too low to control the outbreak of Delta.

The study also included an analysis of a progressive vaccination rollout, finding that if even 40 percent of the Greater Sydney population was fully vaccinated by mid-September, a stricter lockdown needs to continue until then to control Delta. In NSW currently only 16.9 percent of the population is fully vaccinated.

  • Current social distancing in Greater Sydney is estimated to be up to 60 percent from 40 percent a fortnight ago but this is not enough to control Delta sufficiently within one month (which required 80 percent social distancing compliance).
  • The modelling also shows 10-15 percent of people are not observing social distancing restrictions, despite not being essential workers.
  • Fully vaccinating even 40 percent of the population by mid-September would still need to be complemented by a strict lockdown continuing until then.
  • The current social distancing levels estimated by the model are also supported by the real-world mobility reports (Google).

“While in the last fortnight social distancing compliance appears to have increased to 60 percent from 40 percent, this level is still inadequate for the control of the Delta outbreak,” said Professor Prokopenko, from the Faculty of Engineering.

Fig 1.a Demonstrates the inadequacy of current social distancing compliance which is currently at 60 percent in Sydney. Credit: Professor Mikhail Prokopenko.

“To adequately suppress the outbreak, 70-80 percent of residents in Greater Sydney must comply with social distancing, however we are just not seeing those numbers yet.

“What is most concerning is that our model showed that even when we take into account essential workers, 10-15 percent of the population is still not doing the right thing which means we could be stuck in lockdown for quite a while longer.

“The accelerating vaccination rollout will begin to make a difference in a few months, but at this stage a tight lockdown makes a larger impact and needs to continue.

“The main takeaways are people should continue to stay at home as much as possible, minimise their interactions outside households, and get vaccinated.

“No one wants to be in a position where we are still in a lockdown at Christmas. Australia needs to emerge from this and the only way to do so is to go hard and thoroughly.”

What does 80 percent social distancing look like?

  • Compliance with 80 percent social distancing would mean that 4 out of 5 people must drastically reduce their contact with others; in doing so they need to reduce their activities outside of households to just 10 percent of what they normally do.
  • Crucially, 80 percent of social distancing also means that many services currently deemed essential would need to be included under the lockdown restrictions.
About the modelling:
  • The study was modelled up until 25 July.
  • No specific areas in the Sydney metropolitan area were examined in detail.
  • Using a re-calibrated agent-based model, the researchers explored a feasible range of non-pharmaceutical interventions, in terms of both mitigation (case isolation, home quarantine) and suppression (school closures, social distancing).
  • The pre-print paper has not been peer reviewed and is submitted to a leading journal for peer review and publication.
  • The model it uses was published last year in peer-reviewed journal Nature Communications, and a follow-up study of vaccination uptake is accepted for publication in peer-reviewed journal The Lancet Regional Health – Western Pacific.

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