Thread by @BillHanage

This is a completely reasonable request about what recent UK (and other) data means for the pandemic, and in particular BA.1 and BA.2 (let alone BA.3 which, yes, is a thing). Here goes 1/n

https://twitter.com/ViktorWerbowski/status/1486144999976841216

BA.1 and BA.2 (leaving 3 aside for this) are *both* omicron. They are deep branching cousins within the lineage, separating almost a year ago (phylogenetic types don't at me, this is in general terms) 2/n

Now they can be distinguished using this neat property of one of the diagnostic tests. BA.1 has a mutation which means some tests produce a weird characteristic result called Spike Gene Target Failure or SGTF. Most other circulating viruses (including Delta and BA.2) don't 3/n

As it happens, SGTF was also a property of alpha, about a year ago. Changes in the proportions of cases with that property were an early sign of alpha taking over. Later, we saw the proportion of SGTF results dropping as delta (which did not share that property) became common 4/n

It's like successive variants are distinguished by easily detected fashion choices, as if they were Gen Z rejecting millennials' skinny jeans (and millennials rejected the 90s). That is the context for this 5/n

https://twitter.com/jcbarret/status/1486087643632971779?s=20

So - BA.1 which has been the great majority of omicron so far produces a SGTF result. BA.2, doesn't. Therefore when you see the proportions of tests returning SGTF falling away, that suggests BA.2 is increasing 6/n

BA.2 has been increasing in Denmark which has good genomic epi - though no.s of recently sequenced samples relatively small, so any bias towards checking out odd results (non-SGTF) matters. No idea if that has actually been contributing @K_G_Andersen? 7/n

https://twitter.com/K_G_Andersen/status/1485784424729886722?s=20

This is the context in which evidence BA.2 is increasing in the UK, which has a lot of infections as well as very good surveillance, is significant. Huge numbers of BA.1 infections have been dropping but have reached a plateau for now. Not predicting which way that will go 8/n

Probably not helped by this. Note that infection control in schools, never especially serious in the UK, was recently scaled back. There *are* ways to reduce transmission in schools to minimal though not zero levels if resources are available 9/n bbc.com/news/education…

Am I worried? Well any rapidly transmitting lineage is serious because of the disruption it can cause. The severity of BA.2 is yet to be established. My expectation is that it is less serious in those with more prior immunity 10/n

BA.1 and BA.2 are both omicron, but they are pretty different. It remains to be seen what degree of immunity each will generate to the other. This is what I am watching for and what will matter for the future of the pandemic (as well as whether delta becomes extinct) 11/n

Finally, is BA.2 serious? Yeah. But BA.1 was serious. There's a balance between jumping at every curve ball the virus throws us and keeping a cool head. We'll understand more soon. For now, remember that the best thing you can do especially if you're older, is get boosted. END