RT @TRyanGregory
The first XBB was a recombinant between two BA.2 lineages (BJ.1 x BM.1.1.1).

Here's an excellent thread by @firefoxx66 explaining recombination.

https://twitter.com/firefoxx66/status/1587762412110974976?t=8j8yxK5jRadg_SxbChhWKw&s=19

Dr Emma Hodcroft on Twitter

“You might be seeing a lot about XBB these days, & we're in the process of adding it to @nextstrain, Nextclade, & https://t.co/wVE7ubYBoy (as 22F). You might also be hearing it's a 'recombinant' - but what does that mean? Let's take a look. 1/9”

Twitter