[LINK] The Doherty Model

Richard Archer rha at juggernaut.com.au
Fri Aug 27 11:22:53 AEST 2021

Since we're all now amateur epidemiologists, some other assumptions 
which caught my eye in the Doherty report:

p10: "partial TTIQ effectiveness" is based on 700 cases per day. At 
thousands of cases per day there will be effectively no "TTQ", just the 
"I" provided by lockdown measures.

p22: assumption that delta and alpha variants are equally severe. In 
contrast, the Sheikh paper referenced in the Doherty report finds delta 
is "associated with an increased risk of COVID-19 hospital admission: 
hazard ratio 1.85".

p30: assumption that children aged 5-14 show reduced onward 
transmission, seems to be invalidated by data from current Victorian 

p40: assumption that cases are infected but not infectious for 2.5 days, 
data from Victorian outbreak suggests 1-1.5 days

p40: asymptomatic cases are 50% less transmissive, claimed without 
supporting data

p41: it is unclear whether deaths at home are modelled, or only deaths 
within the healthcare system

p20, table 5.6: This shows 5.4% of unvac <16 yrs developing a 
symptomatic infection but only 2.8% of unvac 16-39 yrs developing a 
symptomatic infection. This is clearly misleading and could be due to 
the 180 day limit on the forecast.

Each of the assumptions above result in the model predicting a much 
slower rate of transmission within the community. And therefore 
predicting a flatter curve, lower peaks, less strain on the health care 
system and greater effectiveness of TTIQ. These factors are all mutually 
reinforcing and synergise to produce a socially acceptable outcome.

While I acknowledge that we can't remain locked down forever, I am 
doubtful that the reality over the next 6 months will look anything like 
rosy picture painted by the Doherty modelling.

On the up side Stephen, Table S2.5 represents a 92% reduction in 
mortality rate from the starting point of approx 1%, so a final 
mortality rate of 0.1% rather than your interpretation of a total 
mortality rate of 8%.


On 2021-08-27 01:59, Stephen Loosley wrote:

> The Doherty Model National Plan
> https://www.doherty.edu.au/uploads/content_doc/DohertyModelling_NationalPlan_and_Addendum_20210810.pdf
> Quote: (Page 13)
> "Dynamics and consequences given timing of transition to Phase B
> "Epidemic simulations assume a population size of 24 million. Infection 
> outputs reflect the range of results observed across 20-30 separate 
> model runs for each scenario. We assume that a single outbreak 
> involving 30 individuals initiates community transmission at the time 
> of transition to Phase B, once target vaccine coverage is achieved. 
> Each simulation is run for 180 days after this initiating date ...
> "Figure 2.1: Epidemic growth to 180 days given transition to Phase B 
> leading to established community transmission for the threshold 
> coverage targets of 50, 60, 70 and 80%, with vaccine allocation 
> according to the 'Oldest first' strategy.."  (end quote)
> Now, two of their four scenario graphs barely flatten off at 60,000 new 
> infections a day after their 180 day study limit.
> In other words ..
> The Doherty Model does not even guess at our likely opened-up Phase B 
> daily infection rates will be after six months ..  other than to note 
> that the predicted infection rates will be something more than 60,000 
> people infected every day in Australia.
> On Page 25, the Model for Delta predicts if everyone is fully 
> vaccinated, between 8% and 10% of Australians will die.
> That sounds like a wonderful plan for opening up, Mr Morrison.
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