How are coronavirus case numbers tracking against Melbourne’s step three reopening targets?

Melbourne has successfully reached its step two reopening target, intensifying the focus on driving down the crucial 14-day average so the step three target can be met.

When Melbourne moves to step three, some of the changes would include the five-kilometre movement limit being lifted, cafes reopening for outdoor dining, and up to 10 people being allowed to meet in public.

Melbourne's step three target for reopening is twofold: the 14-day average for all of Victoria has to drop below five and there must be fewer than five mystery cases statewide over the previous fortnight.

Originally, the earliest date the metropolitan region could have moved to step three was October 26, but because the 14-day average has plummeted beyond initial expectations, that date has shifted to October 19.

Here is how the state's 14-day average is tracking against Melbourne's step three reopening target. The blue line on the chart represents the 14-day average, and it has to descend into the green zone under five to reach the step three target.

The goalposts have shifted slightly with the step three target. For step two, the 14-day average used was based on cases in metropolitan Melbourne, but for step three the average encompasses all of Victoria.

Fortunately, the 14-day average in regional Victoria is so low at the moment that it doesn't bump up the average that much. The 14-day average for metropolitan Melbourne is 20.3 and for regional Victoria 0.6. Add those two numbers together and we get a statewide average of 20.9.

There also has to be fewer than five "mystery" cases statewide over the previous two weeks. These are coronavirus infections that were acquired locally that cannot be traced to an outbreak or specific case, which suggests the virus is circulating in the community. Sometimes these cases are also referred to as community transmission cases.

Here is how the number of mystery cases has been tracking against the step-three reopening target. In this chart we have used a red line (that should make it easier to tell the two graphs apart) to represent the number of mystery cases, and Melbourne's aim is to propel that line into the green zone at the base of the graph:

The Age will be updating both of these charts on a daily basis and will regularly post them on the coronavirus live blog until Melbourne's step three targets are met.

As of September 28, there had been 31 mystery cases recorded over the previous fortnight, all of which were recorded in the Melbourne region.

The 14-day tally for mystery cases in regional Victoria dropped to zero on September 18 and has stayed there since. This essentially means that all 41 new coronavirus cases recorded in regional Victoria this month could be traced back to an existing cluster or that the people who tested positive there were close contacts of an existing case.

(There is one slightly confusing little disclaimer for mystery cases, which is worth briefly explaining. The number that was updated on Monday morning by the Health Department is 31 mystery cases, which includes people who tested positive for COVID-19 between Saturday, September 12, and Friday, September 25. There is a slight lag there, because it typically takes health authorities a few days to investigate the infection source. Once the numbers come down even further, that lag will likely start to disappear.)

Once the 14-day average has been driven below five and community transmission has in effect been wiped out, Melbourne can then move to step three. Here's how life would change once step three has been climbed:

The final step for both metropolitan Melbourne and regional Victoria is for there to be no new coronavirus cases recorded statewide over the previous two weeks. This is what the final step entails:

How Melbourne and regional Victoria reached their previous targets:

These graphs have been appearing regularly on The Age website and our daily coronavirus blog over the past few weeks. Now that Melbourne and regional Victoria have met their immediate targets they have been retired, but it's worth including them one final time as their victory lap.

When the state's road map for reopening was announced on September 6, the step two target set for metropolitan Melbourne was to drive the 14-day average down to somewhere between 30-50 by September 28.

Back then the 14-day average for metropolitan Melbourne was sitting at 90.4; it's currently 20.3, and managed to the state government's target.

The target set for Monday was 30-50 cases, and as you can see from this graph, Melbourne has more than met that goal:

Meanwhile, regional Victoria reached its step three target of a 14-day average below five and virtually no community transmission on September 16:

When was the 14-day average for Victoria last below five?

Victoria's 14-day average for new coronavirus cases rose above five for the first time on March 18, and since then there have been only six days when it has dropped below that threshold:

Back on March 18, the infection rate was increasing. There were 27 new cases confirmed statewide, bringing the tally up to 121 cases in total recorded in Victoria.

After the first wave started to subside, there was a six-day window when the state's 14-day average dropped below five again, between April 28 and May 3. It picked up again largely as a result of the Cedar Meats outbreak in Melbourne's west, which ended up being connected to more than 100 cases.

It got agonisingly close to dropping under five during the middle of June, just before the second wave took off.

But in some ways, this graph likely sets the bar too high for the 14-day average, because until mid-July a sizeable proportion of cases were from returned travellers. It is not possible to get a breakdown from publicly-available Health Department data that disentangles new overseas-acquired and locally-acquired cases on a day-to-day basis.

Victoria's 14-day average is currently at 20.9. The last time it was this low was on June 27, when case numbers were rising, and within a week, 10 Melbourne postcodes were sent back into lockdown.

Note: I have opted to use a linear y-axis on the graphs rather than a logarithmic one. A logarithmic scale is indeed better for showing exponential growth and decay, but can confuse readers who are used to reading graphs with a linear scale.

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