What the Doherty Modelling Really Shows About Opening Up at 80% Vaccination

New Australia Institute analysis of the Doherty Modelling shows that while vaccination rates of 80% are essential to protect the community, so are other measures such as the ability to contact trace effectively and other little-analysed assumptions and outcomes of the model.

Key Findings:

  • While high vaccination rates lead to a significant reduction in the spread of COVID19, hospitalisation and deaths, the Doherty Modelling also makes clear that lifting restrictions on people’s movement, mixing and mingling when 80% of adults are vaccinated will lead to up to 40,000 Australians per day becoming infected
  • After 80% of adults are vaccinated, lockdowns will still be a common feature in Australia, sick days and home isolation will be a relatively common occurrence (between 5,000-18,000 Australians will be absent from work and in mandatory isolation 150 days after 30 new cases are reached), and over 760 deaths are expected from the virus
  • Most significantly, the Doherty modelling results are based on the assumption that the effectiveness of the ‘Test, Trace, Isolate and Quarantine’ (TTIQ) system never deteriorates below the level during Melbourne’s second wave infections that saw daily cases top 700 per day; NSW case numbers have already topped 1,000 per day, and unlinked cases numbered more than 800 daily cases the last time unlinked case data was publicly announced

“The Doherty Modelling does not consider what the risks are to a state with zero cases opening up to a state that has thousands of unlinked cases circulating in their community,” said Richard Denniss, chief economist at the Australia Institute.

“The modelling is based on a hypothetical national outbreak that is evenly spread across Australia, but the question that State Premiers, and the Prime Minister are now facing is what should the covid-zero states do? It might be inconvenient to say this, but the Doherty Modelling simply doesn’t help answer that question.

“The Doherty Modelling was conducted several months ago, back before the current big uncontrolled outbreak in NSW. You can’t blame the Doherty modellers for failing to anticipate that the NSW Government would do such a poor job of controlling their outbreak. But you can blame politicians and business leaders who are using the Doherty Modelling to justify opening interstate travel when the modelling provides no clear evidence that it would be safe to do so.

“Models always contain simplifying assumptions. The fact that a model has simplifying assumptions doesn’t make it a bad model, but what is bad is using a model that assumes a problem cannot arise to assert that you don’t have a problem.”

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