recombinant strains, an UK Health Security Agency (UKHSA) study revealed that two different combinations of Delta and BA.1 are XD and XF.
The third is XE. XD is the new name for the French Delta x BA.1 lineage. It contains the Spike protein of BA.1 and the rest of the genome from Delta.
It currently comprises several 10s of sequences. XF is a UK Delta x BA.1 lineage. It has the Spike and structural proteins from BA.1 but the 5' part of its genome from Delta.
It comprises several tens of sequences currently. XE is a large UK BA.1 x BA.2 lineage. It has the Spike and structural proteins from BA.2 but the 5' part of its genome from BA.1.