As Scott Morrison leans on ‘optimal’ vaccine modelling, the epidemiologists he commissioned say they can’t predict a return to normal. By Rick Morton.
Morrison’s figures do not predict an end to lockdowns
There is no normal. The figures don’t provide for it, mostly because they can’t.
When Scott Morrison announced his four-phase road map out of Covid-19, he included phase C as the period when lockdowns would no longer be required and phase D as the period when Australia would be essentially as it was before the pandemic.
But when it came time to provide the scientific backing for national cabinet’s announcement, there was a problem.
Designing models that could account for the final two phases simply was not possible. There were no figures to put to it.
“So I guess, the reason we stopped where we did was we said six months is a long time in this pandemic,” Professor Jodie McVernon, director of epidemiology at the Doherty Institute, who led the scores of epidemiologists and public health modellers working on the project, said during an online press briefing late on Tuesday.
“If you look at the last six months, a lot has changed. You know, what we’ve evaluated and assessed is how far we think we could get with 80 per cent vaccine coverage based on the current circulating strains and assuming the population stays on board with behavioural measures and other things.
“Beyond that, we think it’s just too hard to know what will be happening in the external context for us to be able to really meaningfully inform that assessment.”
When pressed by The Saturday Paper, McVernon smiled. “We declined to make an assessment for [phase] D and I think the prime minister was happy that we had good grounds for saying that.”
Earlier the same day, the epidemiologist appeared via video link at a press conference in Canberra. She was joined by the prime minister, Scott Morrison, Treasurer Josh Frydenberg, leader of Operation Covid Shield Lieutenant-General John Frewen and the nation’s chief medical officer, Paul Kelly. The group announced the modellers’ detailed analysis of moving to a “post vaccination” phase B, which would require ongoing “light” social restrictions and “unlikely” lockdowns.
“So, last Friday I announced Australia’s plan to live with the virus. I announced the whole country’s plan to get us back to that position where we can ultimately live with this virus, in the same way that we live with other infectious diseases that are present in the community, and we can get on with our lives,” Morrison said.
“The targets that are part of this plan, the vaccination targets of 70 per cent to get to the next phase and 80 per cent to phase C, are based on the world’s best scientific analysis and economic advice.”
Even as McVernon implored others to see the modelling as “hypothetical scenarios, a thought experiment” and “not a prediction” the mere discussion of vaccination thresholds provided cover for some leaders to talk about easing restrictions in the middle of an outbreak.
At the start of last week, New South Wales Premier Gladys Berejiklian appeared to suggest the state could regain “some freedoms” if half of its adult population – equal to six million doses of vaccine – was fully inoculated by the end of August. The figure itself is on track to be achieved, with the state having delivered four million doses already and getting through half a million shots each week.
“The challenge for us is we need to do better than keep the virus at bay,” Berejiklian told reporters during Wednesday’s Covid-19 briefing.
“We need to get those numbers down. And the lower the numbers get, and the higher our vaccination rate by the end of August, gives us options as to what life looks like on August 29.”
At the same press conference, however, the premier also conceded what is perhaps an obvious point: “I’m not going to rule out case numbers getting worse,” she said. “I actually think they will get worse. If you look at the number of people infectious in the community, it indicates that perhaps we haven’t reached our peak.”
On Thursday, daily case numbers jumped to a new outbreak high of 262.
The messages were confusing, at best. The state’s chief health officer, Dr Kerry Chant, put it diplomatically during Wednesday’s briefing: “I think it’s too soon to talk about living with Covid. Vaccine coverage levels are not high enough and, as the premier has said, we need to get those vaccine coverage levels up at 80 per cent before we can have that discussion.”
Based on current projections, Australia is on track to achieve 70 per cent full vaccination coverage by the end of this year. In some states, such as NSW and Victoria, that could come as soon as November. In the NT and ACT, sooner.
Nobel laureate Professor Peter Doherty, from whom the modelling institute takes its name, tells The Saturday Paper that this is a key variable.
“The additional variable we haven’t had in any of the Australian situations is rolling out the vaccine pretty fast,” he says. “The Pfizer vaccine gives pretty good protection after one dose but even with that we are waiting for two to four weeks to get that really working. The immune response takes at least two weeks to start producing antibodies and after a month you’re probably looking reasonably good.”
Asked what that means regarding Berejiklian’s suggestion that restrictions could ease with 50 per cent vaccination coverage, Doherty said he couldn’t see it being possible.
“Certainly the models don’t say that, do they,” he says. “I have great empathy for them [NSW] and the situation they’re in, but it is very clear they did not lock down soon enough or hard enough and I can’t see them getting out of this in less than two months, personally.
“If they open up at 50 per cent, that would be insane. Even at 70 per cent they are going to have to be massively careful.”
One thing the national cabinet modelling makes clear is that with “baseline” levels of social and behavioural restrictions, the Delta strain of the SARS-CoV-2 virus enjoys “rapid epidemic growth” even at 50 and 60 per cent vaccination coverage.
“Not possible to constrain outbreak with moderate lockdown,” the report warns for both these thresholds in red shading in its technical appendix.
In these scenarios, “baseline” measurements were taken from NSW in March this year, when only minimal density and capacity restrictions were in place.
Only at the 70 and 80 per cent thresholds do we see “substantial transmission reduction”. Even then, overlaid restrictions will be needed to bring any potential outbreaks under control.
Morrison, backed by infectious disease experts, wants to see Covid-19 eventually treated like the seasonal flu. The modelling provides some scenarios that illuminate just how dangerous the Delta strain is even at these higher vaccine targets. Were an outbreak seeded at 70 per cent vaccination, without further controls, McVernon says there would still be about 2000 deaths in six months. If vaccination was at 80 per cent, 1300 people would die.
“This is a scenario where we roll vaccination out and we stop at 80 per cent. So that’s it. And then we let things unfold from there. Clearly, we’re not going to stop at 80 per cent,” she said on Tuesday.
“We would be still looking to target those groups who have missed out. In every country, we’ll see that if we only get to a certain level, that we will continue to see outbreaks of disease in the unvaccinated population. And so basically, if we stop at 80 per cent and we just let it sit and we don’t do anything else and we don’t have optimal TTIQ [test, trace, isolation and quarantine] and we don’t have additional public health measures, those people will eventually get infected.”
Grattan Institute health and aged-care program director Dr Stephen Duckett tells The Saturday Paper that “advice can be used in strange ways”. He cautions against how the government is using the report.
“The Doherty paper is good in that it showed that if you make different assumptions about TTIQ, you get different results,” he said. “But what government did was choose the ‘optimal’ assumption, rather than a more realistic one, and hid that choice by delaying the release of Doherty until after it released its ‘plan’.”
By choosing the “optimal” assumption for testing, tracing and isolation/quarantine, Morrison has been able to paint a picture that looks very close to freedom for Australians. But the Doherty modelling, which included work from the Walter and Eliza Hall Institute, Monash University, Curtin University, Telethon Kids Institute and UNSW Sydney, is not so certain.
When outbreaks take hold, the scientists assume TTIQ capability suffers from “reduced effectiveness … because public health capacity is finite”. Under an 80 per cent vaccination scenario, the report is careful to underscore that low public health measures may be enough to control an outbreak. But to reduce the transmission potential of the Delta strain below one – similar to a virus reproductive number, below one demonstrates control – the Doherty work indicates moderate public health responses including stay-at-home orders will be needed at 70 per cent and possibly even at 80 per cent.
That is not what is being promised by the prime minister, who insists lockdowns would be rare and then only “highly targeted” with 80 per cent vaccination rates.
“This is very much about evidence provision, it’s not advocacy,” McVernon says. “And what government picks up and does with the modelling is another beast entirely.”
Crucially, the researchers have only had time to work on a model that assumes a uniform national response. That is far from reality. The next step, McVernon says, is to go smaller and map scenarios for different jurisdictions and subpopulations, especially those that remain at greater risk.
“TTIQ response capacity varies markedly by jurisdiction,” the report says, “based on the size of the public health workforce and related laboratory capacity, both of which are critical to rapid case identification for the purposes of case isolation and contact tracing.”
McVernon says the “strong conclusion” of the report is to “highlight the artificial nature of that assumption” of uniformity.
She points to the “high probability of overlap of subpopulations with groups at highest risk of transmission and severe outbreaks” and says “we’re seeing those epidemics rage in the United States right now”. In the report, she says: “We were very strongly messaging the importance of attention to small areas.”
In short, as long as some groups remain at higher risk, so does the country.
The Grattan Institute’s Stephen Duckett says if we assume the national cabinet plan is supposed to be a road map “then it is a very risky road map” – even with the rigorous modelling conducted after the fact to back it up.
“If you look carefully at our report, you’ll see that we don’t think 80 per cent is enough,” he tells The Saturday Paper.
“ ‘Optimal’ is, I think, the new word for ‘gold standard’. I would be very cautious about assuming test, trace and isolation is optimal and there is certainly no evidence quarantine is risk free.”
In the Doherty modelling, the researchers use a baseline reproduction number for the Delta strain of 6.32. For context, the most transmissible virus in humans is measles, with a basic reproductive number of between 12 and 18. Smallpox was three, polio between four and six. Seasonal flu is slightly more than 1 and swine flu 1.2 to 1.6.
However, a leaked memo from the US Centers for Disease Control and Prevention, obtained by The Washington Post late last month, shows the reproduction number for Delta may actually be as high as 9.5.
That is exceptionally high compared with other coronaviruses, and potentially more than twice that of SARS.
With light public health measures in place, the Doherty team measured an effective reproduction number for the strain in NSW – that is, the transmissibility when control measures are taken into account – of 3.2. This is deliberate, McVernon says, because they wanted to use data from Australia to inform only an Australian response.
For now, it is as good as the modelling is going to get. It will need to be updated if more virulent strains or “vaccine escape” variants of the pathogen arise.
It will be a long and difficult race between vaccination coverage and new developments with the virus itself. Late on Thursday, Victorian Premier Daniel Andrews announced yet another seven-day lockdown as eight new mystery Covid-19 cases were discovered. Meanwhile, Scott Morrison is holding tight to the outbreak modelling, taking it as confirmation his road map will work and put an end to yo-yoing shutdowns such as in Victoria.
The prime minister’s public statements have included generous interpretations of the evidence provided to national cabinet.
“Australians want to get on this path so we can live with this virus and they can return to a life they knew, as far as possible,” he told reporters on Tuesday.
“One thing that you don’t do in a pandemic like this is pretend that you can know everything and that you take tools off the table. But the need for those tools, as the modelling shows and the evidence shows, is highly unlikely. Highly unlikely. And certainly, once you get to 70 and 80 per cent, I think that evidence is very clear.”
Not if you ask the woman who did the work, however. Her view is vastly more tempered.
“A lot of us are still pining for a return to life as it was,” McVernon says. “To me, the message is: ‘There is no Freedom Day.’ ”
This article was first published in the print edition of The Saturday Paper on Aug 7, 2021 as "Where to next?".
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