COVID-19: Day 111:Getting better, but too slowly.

Warning: Discussing death is difficult, and if you feel you will be offended by this discussion, please don’t read any further.

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This post looks at today’s data (Day 111) and clarifies the meaning of the data classification “New Cases”.

This change gives a small downward trend to the predicted number of daily deaths. The slowness of this trend – if continued – would result in our national ordeal lasting through to mid-June, with a final death toll in excess of 40,000.

‘New Cases’

In my previous posts (12, 3), I have been predicting the number of hospital deaths one week ahead of time by reasoning that mortality from COVID-19 hospital admissions is around 20% and so 20% of new ‘Cases’ become ‘Deaths’ after 6 days on average.

One important qualification to this prediction is that ‘New Cases’ are evaluated in the same way across the period. In fact the way the statistic for ‘New Cases’ is derived was changed on April 11th (Day 101 of 2020).

Pillar 1 & Pillar 2 Testing

I had been alert to this possibility, but I only became aware of this change yesterday during the government briefing, when they showed this slide.

Slide2

I searched for the data on line but could not find it.

[Update: I found the slides from the daily government briefings here.]

So I captured this by freezing a replay of the presentation and then pressing ‘Print screen’ on my computer. I then typed the number of cases from the blue and orange categories into my spreadsheet.

  • Initially, ‘New Cases’ cases were all deduced by so-called Pillar 1 testing (blue). This is mainly the hospital tests of new admissions.
  • From March the 29th, a small number of cases deduced from Pillar 2 testing (orange) of health care staff were being taken, but these were not included with the Pillar 1 data.
  • From April 11th, the increasing number of cases deduced from Pillar 2 testing (orange) of health care staff were included with the Pillar 1 data.

The effect of this made it seem as if the number of cases from Pillar 1 testing – the statistic we would expect to correlate with later deaths – was staying high when in fact it is slightly declining.

In itself, this is good news. But it is not very good news, because the reduction in cases diagnosed by Pillar 1 testing is not very great.

Revised Predictions

Below I have re-plotted my usual graph but now the prediction for future deaths is based just on Pillar 1 testing

Slide3

The above graph shows various statistics plotted versus the day of the year.

  • the blue curve shows the daily published number of new ‘Pillar 1 tested’ COVID-19 cases.
  • the red curve shows the daily number of COVID-19 deaths in hospital.
  • the black dotted line shows the predicted number of deaths based on 20% case mortality after 6 days.
  • The blue dotted line shows my previous prediction based on ‘New Cases’ diagnosed by Pillar 1 and Pillar 2 testing.
  • The vertical green lines shows the start and end of the first phase of the ‘lock down’

For the part of the curve relating to the last two weeks, the data are not changing rapidly, so we can re-plot the data on a linear vertical scale to see that region in more detail.

Slide4

The above graph shows some of the same data as the previous graph.

  • the red curve shows the daily number of COVID-19 deaths in hospital.
  • the black dotted line shows the predicted number of deaths based on 20% case mortality of Pillar 1 cases after 6 days.
  • the blue dotted line shows my previous prediction based on ‘New Cases’ diagnosed by Pillar 1 and Pillar 2 testing.

What I conclude from this data is that:

  • The number of new cases diagnosed by Pillar 1 testing is falling, but only slowly.
  • Fitting a linear trend to the data (see the graph below) the number of new cases would not be expected to reach zero for another 54 days  – Day 165 (14th June).
  • I do not know why this statistic is falling so slowly, and that worries me.
  • If that trend were followed, the death toll would likely exceed 40,000 – a truly appalling outcome.

Slide5

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Discussing death is difficult, and if you have been offended by this discussion, I apologise. The reason I have written this is that I feel it is important that we all try to understand what is happening.

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3 Responses to “COVID-19: Day 111:Getting better, but too slowly.”

  1. Tim Watt Says:

    Interesting. Doesn’t a lot depend on where or how the currently recorded infections may be happening?
    If the lockdown measures are working and a large proportion of infections are now of close connections to existing cases (ie same households) that population of potential infections might suddenly be exhausted, or quite quickly… whereas if infections are still happening despite social distancing etc. there’s a much bigger potential for the current trend to continue.

    … just a though as I’m no expert.

    • protonsforbreakfast Says:

      Tim, I am no expert either! I am just looking at the data to see what it tells me. To avoid complexity I have tried to focus on what the government call ‘Pillar 1’ testing – which I think is mainly people being admitted to hospital: people who are already quite unwell. I cannot construct the complex models that epidemiologist can, but I would have expected the number of cases to fall faster than this. If I were in charge I would want someone to explain to me what I could do to make that number fall faster.

      Time will tell. Keep well.

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