Omicron’ based on mutations at spike (mutation) residue 452.We @WHO are grateful for the work of scientists across the world who continue to test, sequence, share, analyse, research, discuss SARS-CoV-2 evolution and further sublineages of #Omicron BA.2, BA.4, BA.5Thanks to @Tuliodna @trvrb @GISAID TAG-VE members & many many others https://t.co/COPiW5nh3I Noting that Omicron emerged as three distinct lineages BA.1, BA.2 and BA.3, he said despite the head start of BA.1, we've seen BA.2 overtake BA.1 across the world over the course of January to April.
Variant "fitness" will depend on intrinsic transmissibility and escape from existing population immunity. The first tranche of variants (Alpha, Delta, etc...) largely spread due to increased intrinsic transmissibility, while Omicron spread primarily due to immune escape.
BA.2's advantage over BA.1 appears to be due to intrinsic transmissibility. The antigenically important S1 region of spike is highly similar between BA.1 and BA.2 and we observe similar vaccine effectiveness between BA.1 and BA.2.
And with BA.2's global dominance we expect further evolution to occur on top of BA.2. Speaking on two new sub-variants discovered lately, he added, “It's not entirely clear whether BA.4 and BA.5 are sister lineages to BA.2 or sublineages of BA.2, but this distinction shouldn't matter for assessment of impact on viral circulation"