Doherty report : Why is Australia at odds and what about opening up the country?

PM repeatedly cites the institute’s modeling of 70-80% Covid vaccination rates as Australia’s path to freedom. But what do those numbers really mean? Anyone watching the regular news updates during this Delta outbreak will have heard of the Doherty report. But Australia’s political leaders have different interpretations of epidemiological modeling.

Doherty report : Why is Australia at odds and what about opening up the country?
The Doherty Institute’s modelling considers how Australia’s vaccination rates impact Covid transmission and the health measures required to manage outbreaks. Photograph: Dan Himbrechts/AAP

Anyone watching the regular news updates during this Delta outbreak will have heard of the Doherty report. But Australia’s political leaders have different interpretations of epidemiological modeling.

Given a political battle has broken out between the tiers of government in recent days, it is worth stepping through what this important work does, or does not, say. But rather than the what, let’s start with a why.

Why are governments at odds?

The current dispute reflects the point Australia has reached in the pandemic. Rising vaccination rates will allow governments to start to wind down stringent public health restrictions, including lockdowns. But because we can’t eradicate the coronavirus, and it’s a serious illness for many people, removing restrictions carries risks: rising numbers of infections, rising numbers of serious illnesses, hospitalizations, and deaths. Some state and territory leaders have also expressed concern that we are moving towards opening up when many young people aren’t yet vaccinated. But Scott Morrison wants to get cracking. He declared on Monday the current “Groundhog Day” had to end – and it would end when 70-80% of the adult population were vaccinated. But deciding when and how to open up and “live with Covid” is ultimately a decision about what levels of infections and deaths Australians are prepared to tolerate. That’s why it’s hard. That’s why there are differences.

What is the Doherty report?

The Doherty Institute was asked to prepare a report for consideration by the national cabinet at the end of July. The modeling considers how different vaccination rates in the community and different vaccination strategies would impact the transmission of the virus, and it looks at what level of public health and social measures are required to manage outbreaks. The work was revised on 10 August – that’s the latest version available on the website. The main scenarios modeled in the report estimate how rapidly and how far a single outbreak involving 30 individuals would spread through the Australian population at the time of transition to phase B of the national plan (which is when 70% of the adult population is vaccinated). There is more work being done now looking at whether higher case numbers change the current conclusions. More on that shortly.

Does the Doherty model present vaccination rates of 70% or 80% as freedom day?

Two words.

Absolutely not.

What does it say then?

The Doherty work suggests Australia’s ability to move past restrictions without significant adverse consequences depends on two variables. One: how many of us are vaccinated and in what order. Two: whether or not state health systems can test, trace, isolate, and quarantine (TTIQ) new infections effectively.

What happens with lockdowns?

Well, that depends. Doherty says if TTIQ becomes “partially effective” during a significant outbreak because of pressure on the public health system, then “light or moderate restrictions will probably be insufficient to regain control of epidemics, even at 70% coverage”. It says “prolonged lockdowns would probably be needed to limit infection numbers and caseloads”. But if TTIQ holds up, it’s a different story. If TTIQ remains highly effective then the modeling finds it is possible to stay on top of outbreaks when 70% of the population is vaccinated by imposing more moderate public health interventions, such as moderate capacity restrictions for public places, rather than stringent lockdowns. If TTIQ remains highly effective, then low public health measures (like capacity limitations, not lockdowns) “may be sufficient for control at 80% coverage”. But if TTIQ can’t keep pace, then public health interventions would need to increase (although likely short of a lockdown).

Will these conclusions change if the work assumes higher caseloads?

Perhaps marginally, but Doherty says higher case numbers are absurd to change the current landing points fundamentally. Thirty cases are quite different from our present reality. But the current Doherty modeling simulations show how an epidemic takes off. It shows that with partially effective TTIQ, even with 70 or 80% vaccination rates, a new outbreak affecting just 30 people would spread through the population until daily new infections peak at 35,000 to 55,000 around six months after the initial outbreak. An epidemic is like a bushfire. It burns until it runs out of fuel. But if the TTIQ remains effective at high vaccination rates, infections spread much less dramatically.

Is the Doherty modeling the only relevant advice?

No. Treasury has contributed a separate assessment of the economic costs associated with restrictions. Treasury’s assessment can be boiled down to two conclusions. One, it is “significantly more cost-effective” to manage the Delta variant “by maintaining a strategy to minimize cases and optimal TTIQ, rather than allowing higher levels of community transmission to take hold.” That line of reasoning puts us in a world of ongoing public health restrictions, although likely short of lockdowns. The second Treasury insight is deploying strictly localized lockdowns in response to outbreaks “is more cost-effective than applying more moderate lockdowns for longer periods”.

What does Treasury say about 70% and 80%?

Once 70% of adults (that’s people over 16) are vaccinated and (echoing Doherty’s caution) “assuming the spread of Covid-19 is minimized” Treasury expects outbreaks can be contained using only low-level restrictions, with lockdowns unlikely to be necessary (lots of qualifiers there obviously). At vaccination rates of 70%, Treasury says “the lowest cost strategy is to use low-level restrictions to minimize cases, without more costly lockdowns”. If this strategy is continued at vaccination rates of above 80%, Treasury estimates the economic impact will be lower again. Treasury notes it has not modeled the economic costs of a severe and widespread outbreak that breaches Australia’s health system capacity but notes the obvious: “It is expected that such a situation would carry very significant economic costs.

So who is telling the truth, Scott Morrison or the premiers?

The prime minister isn’t lying about Doherty, but he’s moving people very quickly past the actually important nuances. At a human level, Morrison wants people to focus on life after lockdowns, and not bog that message down with footnotes, which is understandable given prolonged restrictions have a significant mental health toll. But there’s political brinkmanship here too of the most obvious kind. Morrison is setting up a blame game. If the country doesn’t reopen once we’ve hit 70% vaccination rates, the prime minister wants frustrated people to blame the premiers. Seeing that maneuver coming, some premiers (the people who run health systems that could be overwhelmed) sprinted ahead of the prime minister last week, foregrounding the various risks, identifying the crossroads Australia had now reached. How many hospitalizations are Australians prepared to tolerate? How much serious illness? How many deaths? What about kids?