Thread by @chrischirp

VARIANTS: Everyone knows that Delta is the dominant variant in the UK (almost 100% of cases).

But Delta has continued to mutate & there are several subtypes in the UK (all start with AY).

The most common is called AY.4 - almost 80% of sequenced cases in UK are this type 1/6

So far no Delta subtype has seemed to have had much of an advantage over the others & non-Delta variants aren't getting anywhere
news.sky.com/story/covid-19……

But AY.4 has developed a new mutation (S:Y145H) & that variation (AY.4+S:Y145H) has been growing here since July 2/6

It was spotted by @CorneliusRoemer and he suggested giving it its own designation: AY.4.2 (meaning it becomes an official subsubtype of Delta subtype AY.4).

This designation has recently been accepted github.com/cov-lineages/p…… 3/6

That was 10 days ago, so hopefully it will start showing up in COG & Sanger tracking soon.

It's not growing anywhere near as fast as Delta did & even the *worst* case is only a very moderate advantage (maybe 10%) vs 50% that alpha had over wildtype and delta had over alpha 4/6

And we don't know if it's (a bit) more transmissible than other Delta strains *or* if it just got caught up in some superspreader events that seeded it.

No reason to think it's more immune evasive & might well be nothing. Something to keep an eye on but not panic over. 5/6

Finally, Delta is continuing to mutate into subtypes and subtypes of subtypes.

The continuing high case rates in the UK are giving it plenty of opportunities to do so. 6/6

PS Several others have been watching this mutation over the past few months - I'm tweeting about it now because it has now been designated and it doesn't seem to be an artefact of lineage allocation (unlike the previous AY.3 thing).