Post #1359: Brief update on the British Omicron wave

Posted on December 20, 2021

Case hospitalization rate for Omicron is one-fifth of Delta … still.

The government of the U.K. is still running more than a week behind in publishing total COVID-19 hospitalization numbers.  That doesn’t help in tracking what’s happening with Omicron, because the big runup in new cases in the U.K. happened in the past week.

As a result, I’m still screening news reports, looking for pairs of numbers that I can put together:  Total known Omicrion cases so far, and total known Omicron hospitalizations so far.  The goal being to estimate the case hospitalization rate for Omicron.  So far.

As a benchmark, the recent British data (hospitalizations for the week ending 12/14/2021) show that the case hospitalization rate for delta was about 1.6%.

As of today (12/20/2021), this reporting says 104 persons “in hospital” with Omicron.  That’s not the same as new hospital admissions, but given the short timeframe here, it should be close.

As of yesterday (12/19/2021), this report shows a total of 37,101 total known Omicron cases in Great Britain.

Just crudely slapping those together, ignoring the one-day difference, ignoring “in hospital” (current an inpatient) versus admitted to hospital, I get (104/37101 = )  … wait for it …. a ~0.3% case hospitalization rate for Omicron in Great Britain.  

Or, the same number I got the last two times I did this calculation for Great Britain.

Or about one-fifth of the case hospitalization rate for Delta. 

Sooner or later, people are going to notice this.  I think.  For the time being, just mumble a few words about time lags, incomplete data, vaccination rates, and move on.

A break in trend, just over three weeks after the first Omicron case?  Where have I seen that before?

Something else caught my eye as I was working through this.

Take a look at the graph of new cases, by report date.  Looks like the dramatic rate of growth experienced just a few days ago … stopped.

Source:  UK government.

(I use “by report date” counts, because those are complete data.  They are what they are.  By contrast, if you use cases by (e.g.) specimen date, or by reported onset of symptoms, the last few days’ of data will be incomplete, because specimens from those last few days are being processed.  That is, I need to avoid using the time series that naturally tails off at the end, no matter when you look at it.)

The break in trend is clearer if I zoom in to the six-month view:

Source:  UK government.

I wouldn’t normally say anything.  These curves do bounce around quite a bit.  But when the background rate of growth is so high and that growth is expected to continue at that pace by the end of that little plateau you’ve got quite a gap between naive prediction and reality. 

And that’s what caught my eye.  Let me show the formal calculation.  Here’s a simple linear projection (OLS regression) using the seven days prior to the start of the plateau on 12/17/2021.  Three days later, the gap between what you would have expected, if prior amount of increase in daily average cases had continued, and the actual count, was more than 25,000 cases.  Great Britain is still seeing about 90,000 new cases a day.  But if growth had continued, they’d be seeing over 115,000.  The case count is already something like 25% too low, if the pre-existing growth really is going to continue.

I don’t want to make too much out of it, but a) it looks to me like there’s been a break in trend, and b) if that continues another couple of days, I expect people will begin to notice it.

The fundamental reason I am even bothering to pay attention to this is that the South African Omicron wave appears to have been extremely short, and extremely sharp (Post #1358).  They started from scratch — basically no cases in circulation of any type — and South Africa went from first Omicron case to peak in about 3.5 weeks. 

Before I do this next calculation, let me mumble something about South Africa and Great Britain representing two vastly different sets of circumstances, so as to appease the Gods of what passes for Science here.

That ritual now complete, ask this question:  When was Great Britain’s first reported case of Omicron?  My recollection is November 27.  Which means that Great Britain is currently just over three weeks from it’s first Omicron case.


Could be a coincidence.  But it bears watching.  If true, it’ll be fantastically good news.  But a whole lot of British public health officials should have a whole lot of egg on face if, in hindsight, that actually turns out to have been the peak.