Day 17 Scoreboard for Sunday 29th March (7:00pm data):
3,981 total Australian confirmed cases (166 less than the 4,147 we predicted yesterday using the old, out of date, exponential model).
344 new (510 predicted yesterday).
+9% single day increase.
TODAY THE CURVE FLATTENED SIGNIFICANTLY by -2%
+12% daily increase (rolling 3 day average)!
N.B - On Friday we earned our trio of Mitigation Flags yesterday by achieving a -1% or greater reduction in the 3 day average, for three out of four days.
This signaled the START of Phase 2: Mitigation on Day 13: 25th March.
Tomorrow we will switch away from the current Exponential Growth model to a new logistic or sigmoidal one, that factors in a daily reduction in our growth rate of cases.
We will also start to monitor “active cases” based on the sum of our new cases in the last 10 days (only). If we can reduce and maintain our confirmed case growth below 5% for 3 out of 4 consecutive days, this will signal we have entered Phase 3: Suppression.
While we’ve made some encouraging progress this week, we want to caution everyone against overconfidence or misrepresenting these results. A sharp increase in community transmission, increased testing rates or a broadening of the criteria to be eligible for testing could all result in a break-out from the current Mitigation trend, and a return to Exponential Growth phase. This would be signalled by three out of four days with an increase in the 3 day average growth of 1% or more (i.e. the reverse of our Mitigation flags).
Remember, our actions today will only show up in this data in 1 week’s time (at best). The next 7-10 days of confirmed infections are likely already beyond our control. This "inertia" is represented by the light blue coloured cells. If we were to shut down today and completely stop transmission we might (optimistically) hope for a peak of only 8,955 cases in 7 days’ time. The implementation of lockdown in most western countries has been much less effective, with the lag and inertia commonly being longer ( ~11 days in Hubei ). Lockdowns no matter how severe only succeed in reducing the rate of transmission, they don’t stop it in its tracks.
ICU Saturation Estimates:
As of the Day 12: 24th March update, we have revised our estimates of potential ICU saturation in Australia. The only change is the estimated % of cases that require an ICU bed. This is revised down from 10% of cases to 5%, in line with the work of Megan Higgie and Andrew Kahn (reference link below) and emerging anecdotal local ICU data. We are maintaining our assumption of 2,000 ICU beds being available to meet COVID19 demand, which already includes some of the new resources the government is fast tracking. This may be updated in future as more data comes to hand on these resources. This results in a new total case number of 40,000 (to avoid). The arrow and text are changed to purple to highlight this change.
NEW: Signals for Phases 1, 2 and 3
Our chosen “data condition” which will be used to signal departure from the current “Phase 1: Exponential Growth” and commencement of “Phase 2: Mitigation” (should it eventuate) is:
- At least 3 out of 4 consecutive days, where the 3 day average rate of growth reduces by at least 1% (to account for signal noise).
- If this signal is met, the commencement of Phase 2 will be backdated to the day of the first day of reduction in this series.
- A growth rate reduction target of -1% per day will be applied to all days beyond this point. This rate of reduction is likely overly optimistic, given data from other countries, but serves as a good benchmark for effective mitigation (recall Hubei averaged -1.5% per day drop in new case growth for 20 days under full government enforced lockdown, South Korea achieved similar).
- Maintenance of the Mitigation phase is never assured. A return to Exponential Growth phase would be signalled by three out of four days with an increase in the 3 day average growth of 1% or more (i.e. the reverse of our Mitigation flags).
Provisionally, bringing the 3 day average rate of growth of cases to less than 5% and maintaining it below that level for at least 3 out of 4 days will be used to signal the commencement of “Phase 3: Suppression” (should it eventuate). This phase will likely necessitate a change in data and analysis techniques, as yet TBC. Note South Korea still has a steady daily caseload at 1% new cases person.