Australia’s COVID management plan is underpinned by modelling which is effectively obsolete, argue John Quiggin, Richard Holden and Steven Hamilton.
The great economist John Maynard Keynes, when accused of inconsistency on some policy, is credited with saying: “When the facts change, I change my mind. What do you do?”
This point comes to mind in relation to the fractious debate over Australia’s “National Plan” to relax restrictions at 70% and 80% vaccination-rate thresholds.
This plan was agreed to by National Cabinet on August 6 — though apparently with a different interpretation for each government involved.
Underpinning it is modelling by the Doherty Institute, done in July this year. There has been plenty of argument about particular assumptions in the Doherty model. But the more fundamental problem is that it is effectively obsolete.
Delta has changed the landscape
Ideally models of any phenomenon are based on directly relevant data. In recent years the development of techniques for “big data” (large data sets, often derived from administrative records) have yielded a wide range of new insights.
In the case of COVID-19, the data needed for such an approach include evidence on the way in which changes in conditions change the “Reff” — the effective reproduction rate of the virus.
The Reff is a number that indicates the average number of new cases generated by each existing case. It is influenced by vaccination rates, movement restrictions and the capacity of testing and tracing measures to locate and isolate those infected. To avoid an uncontrolled pandemic we need to keep the Reff below 1 most of the time.
When the Doherty Institute undertook its modelling there was essentially no data for Australia relevant to the scenario policy makers are now contemplating.
There had been no sustained outbreak of the Delta variant, and only one extended lockdown to give evidence on the effectiveness of various measures. So the Doherty Institute had to use a theoretical model with parameters derived from a combination of overseas evidence (from countries with experience very different to that in Australia) and the best guesses its experts could make.
We now have a great deal of data on the Delta variant and the effectiveness — or ineffectiveness — of various restrictions, and the…
Read More: Australia’s COVID plan was designed before we knew how Delta would hit us