What if Victoria cannot eliminate Delta this time?
Monday, Aug 23, 2021, 04:42 AM | Source: Pursuit
Lockdown 5 in Victoria was textbook. Outbreak occurred, contact tracing swung into action, cases were found and, over time, the number of daily cases infectious in the community diminished to zero for three days and we emerged from lockdown.
In fact, the majority of cases that have been found have been infectious out in the community and aren’t reducing over time – but rather going up. Even worse is the constant stream of mystery cases that are driving this bad trend.
When there are mystery cases, there will be future cases in the community by definition.
I strongly support the Victorian Government’s decision to go ‘really hard’ by Australian standards with curfews, the closure of playgrounds and childcare, and further reducing essential workplaces.
It would be so great to re-eliminate the virus and wish for a near normal life until the end of the year. But we need to be realistic.
The elimination strategy always had, and continues to have, a planned pivot to living with the virus once we are ready. Ideally, at something like 80 per cent adult vaccination coverage – although personally, I would prefer that to include children as well.
But the virus may be forcing our hand earlier than we planned.
If the hard restrictions in Victoria don’t see a dramatic improvement by 2 September, such as new infections running at less than five cases per day (which seems very unlikely), what should we do?
We could hang tough and keep the number of infections as low as possible by staying in hard lockdown longer. But then the questions remains for how long?
This is wickedly difficult decision making for Governments. It’s about picking the least harmful course of action.
Our COVID-19 Pandemic Tradeoffs modelling group at the Melbourne School of Population and Global Health has done a lot of modelling of this pandemic – but not exactly the Victorian scenario leading up to 2 September.
What we’ve tried to do here is apply plausible daily rates of change that we have modelled and calibrated elsewhere for soft and hard lockdowns. And while this isn’t a model per se, we hope to provide a framework to help all of us think our options through.
THE OPTIMISTIC SCENARIOS
The first figure shows three scenarios that assume we make some progress by 2 September.
In the first scenario, shown in green, we have hit 40 cases per day a week before 2 September, then five cases per day by 2 September – so we come out of lockdown.
And then we get lucky. We have no further incursions and outbreaks from hotel quarantine or from across the NSW border before the end of November when 80 per cent of adults will be at least 10 days-post their second dose and we shift into Phase C of the National Plan.
We all hope this will happen, but it seems unlikely.
The second red scenario starts out the same as the first scenario, but we have repeated monthly incursions requiring repeated fortnightly lockdowns. Our scenario has these lockdowns being effective – so still optimistic in that regard – although it will get easier to stamp out outbreaks as vaccine coverage increases.
Here, we oscillate our way to the end of November with about two months total in hard lockdown.
The third scenario, the grey line, is where some progress has been made by 2 September, but only to the point of 30 cases per day requiring another four weeks of hard lockdown to drive the case numbers down to five per day and, finally, step out of lockdown.
Not great, but a return to zero transmission.
But what about if we haven’t made any progress by 2 September, and the case numbers are still around 50 per day, or worse? What should we do then?
Well, one option is we could stay in hard lockdown, and just wait until the vaccine coverage tips the balance our way and we tip to numbers going down. It’s a similar scenario to the grey line in the first figure – but with longer in lockdown.
There are other options though.
We could let go of hard lockdown, and shift to a soft lockdown. A world where more time is allowed outside, no curfews, you can travel 10 kilometres or more from your home, some retail is re-opened, construction and other industries on the ‘essential’ threshold are started up.
The exact mix would remain to be determined – it would still be far from a full opening up.
Using a Victorian-style Stage 3 lockdown as an approximation of a ‘soft lockdown’, and using the apparent tipping point in terms of vaccine coverage when it is enough to cause numbers in our NSW modelling to start going down, we mathematically arrive at the second figure.
This fourth ‘moonshot’ scenario sees the numbers go up as expected, but then turn and decrease with increasing vaccine coverage.
This moonshot appears to work if the criteria for success is keeping daily case numbers less than 500 on the way to the end of November.
The flip-side, though, is we are in a soft lockdown the whole time until early November. And it is – of course – risky and uncertain.
The fifth scenario is for a two percentage point higher daily percentage change in cases at each point in time (reflecting perhaps a difference in the maths or Victoria getting unlucky with lots of super-spreading events) – that’s enough to quickly see the case numbers hit 500 by virtue of exponential math.
Nevertheless, the soft lockdown moonshot does appear to be an option worth discussing, and doing more formal modelling.
The purpose of this the five scenarios here isn’t to advocate for any particular option.
We hope that the numbers dramatically turn down in the next week, but we need to also start thinking about (and discussing and debating) what our options are come 2 September if the COVID numbers have not dramatically decreased.
A version of this article was first published in the Australian Financial Review.
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