Post #1021: U.K. variant spread remains on track for mid-March 4th U.S. wave

Posted on February 21, 2021

The U.S. is now down 73% from the peak of new COVID-19 cases.  Texas shows no rebound in new case counts yet.





Today’s question is “How prevalent is the U.K. variant in the U.S. now”?

Recall that, based on published estimates from January, and simply projecting forward with the stated growth rates, the U.K. variant ought to account for about 15% of U.S. cases now (third week of February).  That’s per my analysis, which matches all the (then-known) stylized facts about prevalence and growth of the U.K. variant in the U.S (Post #1007).

Every time you see a phrase like “The U.K. variant will become the dominant COVID-19 strain in the U.S. by March”, that’s based on a projection similar to what you see above.  And if that’s on track, then we ought to be seeing that the U.K. variant now comprises 15% of new cases.  Or so.  Based on the last hard data point we had, which was that it accounted for 4% of cases as of the last week of January.  (Per this reference).

So, who has the current data on this?

Oddly, the U.S. CDC appears to be completely useless in this area.  They seem to track the total number of cases that have been identified.  That, by itself, is useless because you don’t know the denominator of all cases that were tested.

The upshot is that I can’t find anything useful from the U.S. CDC.  Near as I can tell, the CDC’s published information just tells you that they are almost kind-of maybe ready to start collecting some information on this some time in the next few months.  At least, that’s how I read this.  So, for whatever reason, all they show now is the total number of “sequences” collected.

It takes a while to track it down but I believe this page from Helix corporation provides the best available data, in the S-Gene target failure graph.  That company very cleverly uses a test that does not precisely identify the U.K. variant, but comes close, and that does not require gene sequencing and so can be done in nearly-real time.

Combining their two tables, my best guess is that the U.K. variant accounted for just over 10% of cases (80% of 13% of samples tested) as of 2/15/2021.  Which puts it absolutely on-track with the second-week-of-February “you are here” line on the table above, in terms of level and growth rate.

The upshot is that the U.K. variant is growing pretty much exactly as projected.  Absent any other changes, we should be prepared for the U.S. fourth wave of COVID to begin sometime in mid-March.

Obviously, that’s not set in stone.  “Seasonality”  might still save us.  Which is equivalent to saying that we might get lucky.  And it’s possible that we’ll be close enough to herd immunity by that time that we’ll see a rapid contraction in total COVID-19 new case rates, despite the increased incidence of the U.K. variant.

But as of now, the smart money bet remains that new case counts will stop falling, and being to rise, mid-March.