Victoria has entered a five-day lockdown to control its growing outbreak of the more infectious Delta variant.
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Christopher Fairley
Professor of Public Health, Monash University
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Lei Zhang
Associate Professor of Public Health, Monash University
Until midnight on Tuesday restrictions mean residents are only allowed to leave home for essential reasons, can only travel five kilometres away from home, and need to wear masks outside the home, among other measures.
Breaking: Victoria has recorded six new cases of coronavirus on the first day of its fifth lockdown of the pandemic, on top of the six cases announced yesterday afternoon. https://t.co/vqoAgc1Phm
- The Age (@theage) 15 July, 2021
We consider the lockdown essential, and we strongly support this rapid action. However, our modelling predicts a five-day lockdown may not be enough.
Instead, we predict at least 30 days of restrictions will be needed before Victoria reaches three days without community transmission.
That's if we take into account current and predicted case numbers, the fact we're dealing with the more infectious Delta variant, and with current levels of vaccination.
The good news is Victoria is more likely to reach these three "doughnut days" sooner if vaccination rates pick up, even modestly.
How did we come up with these figures?
We built a mathematical model based on nine COVID-19 outbreaks across four Australian states (including Victoria) since the start of the pandemic. We posted details online as a pre-print. So our model has yet to be independently verified (peer-reviewed).
Our model allows us to predict - given current case numbers, the particular variant in circulation, and vaccination rates, among other variables - how long public health restrictions such as lockdowns need to last to achieve particular outcomes. Our model also allows us to predict how many cases an outbreak has at its peak.
Models are mathematical tools to predict the future - something, of course, no one can do with 100% certainty.
However, our model differs from others because it considers the difference between mystery cases and cases linked to a known case.
