The Doherty modelling suggests the Government’s COVID reopening plan is reckless
by Anika Stobart, Stephen Duckett
The Prime Minister has released the findings of the Doherty Institute modelling that informed the vaccination thresholds for the National Plan to reopen Australia. It shows that their four-phase plan is extremely risky.
To move to Phases B and C of the plan – where COVID-19 would circulate in the community with only low-level restrictions – there needs to be near-perfect test, trace, and isolate capabilities to keep COVID-19 under control.
If these capabilities are not up to scratch, the only options are either a high death toll, or more lockdowns.
And the policy changes in Phase C – where the government said vaccinated people would be exempt from any domestic restrictions – are not reflected in the modelling. Such exemptions would likely undermine the effectiveness of containment measures.
The Doherty model looked at how different population vaccination levels would reduce the time needed to stay in strict lockdowns and control an outbreak if optimal test, trace, isolate, and quarantine measures, and other baseline restrictions (such as capacity limits) remained in place.
It found that light restrictions combined with test, trace, and isolate measures would not be enough to constrain an outbreak when only 50 or 60 per cent of the population aged 16 and older is vaccinated.
The modelling shows that at 70 and 80 per cent aged 16 and older vaccination rates, baseline restrictions and ‘optimal’ test, trace, and isolate measures would be enough.
It showed that they would more than halve the effective reproduction number – the average number of people an infectious person infects – of the Delta variant of COVID-19.
This represents a significant drop in infectiousness, effectively reducing Delta’s transmissibility to similar levels as the original strain of COVID-19.
The question then is: can these ‘optimal’ test, trace, and isolate capabilities be translated into the real world? It is unclear whether state governments systems are up to it, especially given that tracing is notoriously difficult when case numbers are very high.
The recent hard lockdown in Victoria shows that it felt that it could not rely on its test, trace, and isolate system, even with a low initial spread, because of the infectiousness of Delta.
Relying on ‘optimal’ test, trace, and isolate effectiveness is a highly risky strategy for governments to take, especially given that test and trace capabilities vary significantly across the country, and Australia doesn’t have any effective nationwide infrastructure to make it easier, such as Britain’s National Health Service (NHS) tracing app.
What if the test, trace, and isolate capabilities are not enough? The Doherty modelling showed that under the 70 per cent vaccination scenario, with only baseline restrictions and partially effective test, trace, isolate, and quarantine capacities, there would be 290,000 COVID-19 cases and about 2000 deaths within the first 180 days.
If this spread threatened the health system, state governments would have to impose restrictions such as lockdowns to get it under control, as the plan acknowledges. In fact, the Doherty modelling says in this scenario, lockdowns would need to be in place for 20 to 40 per cent of the time, depending on the age profile of the vaccinated population.
And for Phase C – where the government committed to an 80 per cent vaccination threshold of the population aged 16 and older – there is no modelling on the impact of the policy changes on containment measures.
The government’s plan exempts vaccinated people from any domestic restrictions, even though vaccinated people can still spread COVID-19. Such exemptions would undermine optimal testing, tracing, isolation, and quarantine, and increase the risk of needing lockdowns.
At the same time the plan significantly curtails the ability of state governments to impose lockdowns, again by exempting the vaccinated from them. That is less likely to work than a population-wide lockdown, not only because vaccinated people can spread COVID-19 but because enforcement would be very difficult.
The government is undermining its first line of defence – testing, tracing, isolating, and quarantine – and its last line of defence – lockdowns – at a level of vaccination where its own modelling suggests both of those lines of defence will be important.
The good news is the government has released the modelling that informed its thinking on the thresholds for Phase B.
The bad news is that the plan – which was crafted by governments, not by the modellers – is reckless.
The national cabinet should not be pulling a trigger too early and consign Australia to even more lockdowns and a higher number of COVID-19 deaths – or a combination of the two.
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