Saturday, December 25

Christmas 2021 - a complete set of Covid charts for Australia

At Christmas 2019 I was newly retired and completely unaware of the global pandemic that was already nascent in Wuhan China. The past two years have been a rough, roller-coaster ride. The shock of the initial cases and deaths. Victoria's second wave. The serendipity that flattening the curve managed to achieve the elimination of local transmission. A slower start to mass vaccination in Australia compared with other high income nations. The arrival of the more infectious Delta variant, which proved challenging in NSW and Victoria, and the resulting interstate travel restrictions. And in the past four weeks, the arrival of the even more infectious Omicron variant. Largely as a result of Omicron, 14 per cent of all Australian cases occurred in the past week.

So far, the case burden of COVID-19 has been felt the most in Victoria, followed by NSW.

Recent case growth with Omicron can be mapped in a few ways. Let's focus on NSW, as it has a longer Omicron growth trajectory. We are seeing daily new case numbers double every 4 days or so in NSW. The effective reproduction number is around 2 in NSW (every infected person infects two others on average).
There have been 2182 deaths in Australia from COVID-19. More than half of these deaths were in Victoria. While the total is a relatively small number by international comparison, it is not insignificant.

Where there has been some good news is in the death rates. Last year during Victoria's second wave we saw 4.3 deaths for every 100 diagnosed cases.

Currently, we are seeing 0.51 deaths per 100 cases in Victoria and 0.38 in NSW, a tenfold improvement on the Victorian second wave on 2020. This can be attributed to a number of factors including mass vaccination and better treatment regimes.
A key policy concern with COVID is the capacity of the hospital system to cope with the peak demand. So far, all hospital systems have managed, albeit with some pressure during the Delta wave in the second half of 2021.

The present concern for hospital systems is the rapidly increasing case numbers associated with the Omicron variant. While the international evidence is that Omicron cases are less severe there are a couple of points of concern. The first is that the unvaccinated in Australia are unlikely to have any natural immunity. The second is that while Omicron might result in less severe disease, the volume of cases may still overwhelm the hospital system. The NSW data suggests that we are not seeing the same rate of hospitalisation (but there are a few caveats here). The picture should be much clearer by new year's day.

Another pressure from the emergent Omicron outbreak is on testing systems. We are seeing increased testing and positivity rates (noting that positivity rates may be impacted by the recent availability of rapid antigen tests).

Finally, let's look at vaccination rates. After a slow start, Australia is among the most vaccinated nations in the world.

As usual, the code for these charts is available on my GitHub site. I use as the data source for these charts.