Tuesday, January 11, 2022

The Omicron COVID wave in Sydney -- in actual practice -- is showing less severe disease risk to patients than seen in the previous Delta wave


 Key messages:

This is the latest announcement from NSW Health about the current COVID-19 outbreak:

How are we to make sense of it?

We know total case numbers may be misleading as testing and tracing efforts are grossly overloaded and many people are taking unrecorded antigen tests at home.

Let's focus on putting the more reliable hospital and ICU numbers in context.

Here is a graph showing how hospital and ICU reported numbers have evolved over time:

Updated 12 Jan 2022

The blue curve shows total hospital COVID-19 patients on the day they were recorded in the NSW health system.

The orange curve shows patients number needing intensive care adjusted to help understand any trends in altered disease severity.

To allow for the later onset of more severe disease needing transfer to the intensive care unit, ICU numbers (orange curve) are those that NSW Health recorded three days after the time point plotted on the graph. They are also multiplied by 5. 29 to allow comparison with total hospitalisation.

 Throughout most of this period, total hospital number accurately predict ICU needs for COVID-19 three days later using the formula

ICU demand=hospital demand three days earlier/5.29 ( equivalent to 19 percent)

But there is good news-- A Christmas Present

Starting 23 December 2021 to ICU curve in orange breaks away from the blue hospitalised total patient curve.

In the last few days (11 Jan 2022) the correction factor needed changed by a further factor of 2.0


ICU demand=hospital demand three days earlier/10.6 (equivalent to 9.5 percent)

This is extremely good news

It confirms that:

  • on the ground in Sydney the SARS-2 Omicron variant is half as likely to cause very severe life threatening disease in hospitalised people than the Delta variant did in September-October 2021
  • the earlier UK experience with lower Omicron disease severity is being repeated in Australia
  • prior NSW Health modelling of the outbreak is close to what is happening in practice now in Sydney

    From this and other evidence, the Pundit can now predict a NSW hospital peak of near 6000 COVID-19 patients and ICU demand peak near 540 severely afflicted patients -- within hospital system capacity it seems.

    The Pundit is very relieved to find NSW Health professionals got it right one more time, and that vaccines and boosters are working so well in Sydney.

    Graph of Dan Babs on Twitter nicely extends and confirms this post with different comparisons. It seems, sadly, that deaths may not correlate well with the welcome ICU trends:

    Updated 13 Jan 2022

    This sharp point on deaths being different to ICU and hospitalisation, and are rising sharply, is an echo of what happened in the UK in January:

    Added note 12 Jan 22 from France, h/t @EricTopol and @nicolasberrod on Twitter

    Merci @nicolasberrod 

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