Lots of talk about the XEC variant lately. It's a fast variant, but I want to emphasize two things.
First, I don't think XEC is much faster than the dominant KP.3.1.1. Germany is the only country w/enough seqs for a reliable growth estimate & it's pretty modest & uncertain. 1/6
First, I don't think XEC is much faster than the dominant KP.3.1.1. Germany is the only country w/enough seqs for a reliable growth estimate & it's pretty modest & uncertain. 1/6
A variant w/such a small growth advantage (assuming it's accurate) takes months to grow to dominance. And such modest advantages do not result in any noticeable change in case levels, so I don't expect XEC to have any real impact. By the time it would become dominant... 2/6
...it's almost certain that some other, more dramatic evolutionary event will have taken place, whether that be another chronic-infection-derived saltation variant or simply further stepwise spike mutations on top of current variants. 3/6
2nd important point: XEC's spike is nearly identical to KP.3.1.1's spike, so there's no real concern about immune escape here.
There are only 2 differences:
#1. KP.3.1.1 has ∆S31 & XEC has T22N. But both introduce glycans & have near identical effects on growth. 4/6
There are only 2 differences:
#1. KP.3.1.1 has ∆S31 & XEC has T22N. But both introduce glycans & have near identical effects on growth. 4/6
#2. XEC has F59S, which KP.3.1.1 lacks. This is the most likely source of XEC's slight growth advantage over KP.3.1.1, but it's not in an antigenically important region & has never been a major factor in any previous variant.
Meanwhile, they share 63 AA spike mutations.
5/6
Meanwhile, they share 63 AA spike mutations.
5/6
In summary, I see XEC as a notable and important variant but not one likely to have a major real-world impact. Others feel differently, and I could be wrong. We probably won't know for several weeks yet. 6/6
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