Brief JN.1 wave update

There's a mighty judgment coming, but I may be wrong

It’s a few weeks since I last wrote here about the JN.1 wave, and I think that piece (arguing that mixing would play a significant role in slowing down growth) has aged fine. Now that we’re starting to see numbers after the Christmas data lull, it seems clear that we did see a sizeable wave of infections in the run-up to Christmas, but the recent ONS data has shown a convincing peak since then:

Coupled with the fact that we are seeing similar looking peaks in other countries (this is wastewater data from the US for example), I think my thesis of “mixing matters a lot at this time of year” has aged pretty well - certainly there’s no obvious reason you’d expect a purely immunity-based peak to be so synchronised across two continents:

From my point of view, the other positive development is that we have also seen relatively low admissions given the estimated number of infections. Now that we have the randomised ONS survey back, we can crudely compare the hospitalization rate between waves, for example by plotting estimated prevalence at the peak of a wave against “for COVID” beds at the corresponding hospital peak¹.

If you think about drawing a line from the origin (0,0) to each point, the steeper the line, the higher the hospitalization rate. So you can see a big drop in 2021 when the autumn wave met a vaccinated population, and a subsequent further drop in slope as we moved into the omicron waves of 2022.

And now, perhaps, there is tentative evidence that JN.1 has led to an even lower hospitalization rate. Presumably if this is the case then this lower observed severity reflects the high levels of immunity we have reached in the vulnerable population, following several rounds of boosters and previous infections, acting to reduce the worst consequences of infection. I think it’s not definitive yet, but that plot is certainly suggestive to me.

Overall then, what I wrote six weeks ago, when first being explicit about the fact that we were about to move into case growth, feels like a very good description of what we actually saw:

This is not to say that disaster, lockdown, human sacrifice, dogs and cats living together, mass hysteria is in the offing. While the estimated growth rate is probably higher than anything we’ve seen in the UK for a while, it’s not as high as the BA.5 strain which caused the last really big wave of admissions (in summer 2022). And while there’s likely to be a fair amount of mixing in the lead up to Christmas, as we saw a year ago that tends to drop off in the New Year, so JN.1 might well find it harder to spread then. Since admissions are currently at a pretty low level by December standards, any wave has a fair amount of work to do to even reach the admissions levels we saw last winter.

So, I’m pretty happy with that - I think it’s at least as accurate as other UK-based predictions I’ve seen doing the rounds. (I had a bit of a rant about this on Twitter, but I won’t bore you with it here).

Personally I think the jury is still a bit out on what the shape of the curve will be in the next ONS survey. It’s worth remembering that the curve above only runs up to 3rd January (before schools and offices returned in serious numbers), and that the nature of the curve-fitting part of the estimation process tends to mean that later points can sometimes be revised more.

So I wouldn’t necessarily expect that you can extrapolate that downwards curve at the same rate - I might well expect something flatter (and possibly even growing slowly) in the coming few weeks.

And it’s worth remembering that the most recent hospital admissions numbers may have been been pushed down by the effect of junior doctors’ strikes, so I wouldn’t be surprised to see something of a rebound in “with COVID” admissions next week² .

But overall, it feels like we could be in a lot worse shape right now. It certainly seems hard to argue that we are in a phase of exponential growth at any significant rate. My general feeling is that the Christmas wave may not have done as much damage as some people feared, but it was right for me to raise the likelihood of this wave in advance of it happening.

However, as the evenings start to tentatively grow lighter and we start to move towards spring, my feeling is that it’s long past the point where it’s perfectly reasonable for most people to not have any of this stuff front and centre in their mind any more, even if we may have further rises and falls in the graphs to come in future months.

1. Two minor caveats here: the position of the Jan24 point is somewhat indicative at the moment, because the wave may not be over, but I don’t expect the point to move a huge amount. Also we don’t have “for COVID” beds for the Jan21 wave, so I estimated it by taking 80% of the “total COVID beds” figure, which is roughly consistent with what we saw when we did start getting “for COVID” data in the pre-omicron era later in that year.

2. If routine admissions were being cancelled as a consequence of the strikes, then incidental admissions would presumably be down as a result. I hope this wouldn’t affect the “for COVID” numbers I plotted above so much, but it’s another reason to regard that data point as somewhat tentative.