More Impactful Omicron Sublineages: Virologist Explains 3 Ways Covid Variant Is Evolving | Mint - Mint
Noting that Omicron emerged as three distinct lineages BA.1, BA.2 and BA.3, he said that 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.
With too many Omicron sub-variants circulating at the moment, eminent virologist Trevor Bedford pointed out we are likely to see more impactful sublineages of the variant in the recent future. He further explained 3 scenarios of how the virus can evolve and also added that tt's quite possible to witness "Omicron-like" events in the future too.
Recently, in a series of tweets, Bedford explained that we are already witnessing ‘evolution of new potentially impactful sublineages of Omicron’ based on mutations at spike (mutation) residue 452.
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”
Future scenarios:
- The hypothesis is then that 452R/Q is conferring some additional intrinsic transmission advantage. Distinguishing these scenarios is challenging however and largely relies on assessing neutralization titer in assays with 452R/Q viruses and recent human sera, he said.
- It is now expected that 452R/Q sublineages will continue to expand. As they do so, they may acquire additional mutations with the "winning" sublineage the one that accumulates the best constellation of mutations.
- However, it's also possible for some other mutational constellation to arise (on top of BA.2 or otherwise) and overtake these new 452R/Q lineages.
- This sort of accumulation of mutations that drive further host adaptation and antigenic drift is my general expectation for evolution in the coming months. It's possible we may have additional "Omicron-like" events, but my baseline is this steady "flu-like" scenario.
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21 Apr 2022, 07:54 AM IST