Finally, some unexpectedly good news on community spread in Victoria:
Untrackable new cases in Victoria are drying up. The incidence of community spread cases with an unknown source are every epidemiologists nightmare. So their absence is a marker of how well the restrictions work– and whether the “fire” is under control. It’s cheery news.
Community spread is the number that matters most — more than daily infections. Known cases can be track-and-traced. Unknown cases mean whole clusters are spreading invisibly and restrictions need to be wider. Despite the depressing schedule planned in Victoria, if this reduction in unknown cases is sustained, then other options for pandemic management become possible. The NSW-style-management with intense tracking and tracing may suddenly become an option within weeks. (Though there may be a 50 case spike tomorrow just to prove me wrong.) Tracking and tracing works best at lower levels, and becomes overwhelming quickly as the number of clusters rise.
With strong restrictions, the exponential rise in infections can become an exponential fall. Where before each person might infect three new people, now three people staying home are only infecting one (or something like that). Two lines get extinguished instead of amplified, as the virus runs out of fresh bodies to hijack.
Victorians, no doubt, are fed up to the nth with lockdowns. At least a graph like this shows the end is in sight, and the isolates have achieved something. It augurs well.
Victoria, unknown cases of Covid-19, March to Sept 2020.
Unknown cases in NSW are also graphed (in blue, above) for comparison (and below in more detail). The spread in the Victorian community was vastly larger than what NSW faced in March when many cases were from overseas.
Don’t confuse this graph up for Daily New Cases, which are still coming in this week at 112, 79, 64, 59, 36…. New infections are still popping up, but mostly they are connected to known outbreaks, which are easier to manage (usually).
The Victorian modeling of how long strict conditions need to run apparently doesn’t take this into account. So the harsh conditions are likely to end sooner than expected as long as people stay distant.
The modelling did not attempt to estimate the number of community transmission “mystery cases” in the weeks ahead, nor did it model differing risks of transmission in industries like healthcare and meatworks.
The makeup of cases each day is important in determining the risk of a resurgence.
This is especially promising when we consider how well NSW is doing.
For the last two months NSW has danced with the tiger and kept daily new mystery source cases under 5.
Given that this was in winter, in a big city, this is good news too. This appears to be quite the success with tracking and tracing, and presumably with compliance.
NSW, unknown cases of Covid-19, June to September 2020.
Currently there are a stream of random closures of schools or gyms and resturants. Sydneysiders can have gatherings of up to 20 people at one time. Funerals, with 100. Weddings with 150 people. Large sporting events are limited to 500. Stadiums are at 25% capacity.
The problem is, of course, that NSW is running along a razor thin fence, one superspreader event away from bad news, and while they are moving a lot more than they were during the official lockdowns of April, it is still below normal levels.
Let’s hope the numbers stay this low. At least in Australia, days are getting longer, and the sun and Vitamin D are rising.