In a few weeks the variant has supplanted the previous Delta and become predominant all over the world. And it still is, why it behaves differently: how it evolves and what is convergence
it’s been a year now since, on November 26, 2021, the World Health Organization (WHO) publicly announced the discovery of a new variant of the coronavirus that would take the name of Omicron. Since then in a few weeks, Omicron has supplanted the previous Delta and become predominant in
Worldwide.
Evolution
Until then the main variants had followed one another months apart: the most widespread were Alpha and Delta. But with Omicron everything changed: the first variant to be one year old and even now represents 99.9% of deposited sequences in the world (source WHO week from 7 to 13 November). For now it has not been replaced by other lineages with other abbreviations of the Greek alphabet, but instead exploded into hundreds of sublineageseach of which has its own alphanumeric nomenclature, such as XBB, BQ.1.1 and CH.1 .
What makes Omicron different? It moults very quickly compared to the variants of more than a year ago: for the first months after its birth, the sub-variants produced replaced each other; thus the first version, BA.1, was replaced by BA.2, then by BA4-BA.5. Now it is rather about one swarm of derived strains which gradually offer greater resistance to our immune system and are eluding some antibodies produced by previous infections by Omicron itself.
The convergence
There speed of mutation internal to Omicron its true evolutionary advantage. The prevalence of Omicron in the world has helped in this sense: thanks to the high number of infections, the virus has had billions of opportunities to mutate. Ben Murrel, computational biologist of Karolinska Institutet of Stockholm, and his colleagues are tracking more than 180 subvariants of Omicron that have mutated independently. The subvariants escape the same antibodies thanks to mutations at the same points of their spike protein, mutations that these variants have developed one independently of the others. It’s called convergence, an evolutionary process leading to similar outcomes that Charles Darwin identified some 160 years ago, when he examined how birds and bats had separately evolved wings that function very similarly. Perhaps the competition going on in the multitude of subvariants to prevent one of them from taking over, at least for now.
BA.5 and all of its lineages continue to be globally dominant, representing the 73.0% of the sequences (WHO source cited above), BQ.1 and his 30 descendants (including Cerberus) are al 27.3%, BA.2.75 (Centaurus) increased to 6.6% And XBB extension (a hybrid of two different subvariants of BA.2) arrived at 3.8% world.
The only (partial) barrier are the updated vaccines
We do not know what the future dynamics of SARS-CoV-2 will be (it seems impossible but we still know little about it), but we know that the type of evolution of Omicron puts at risk above all the stability of monoclonal antibodies, minus that of vaccines, also because they have been updated on Omicron. Studies conducted on people who received the bivalent recallreveal that their antibodies better neutralize BQ.1.1 and other new subvariants, unlike the antibodies produced by the original Covid vaccine. Better, but in a partial way, which means: with a good resistance to the defense against serious illness and death and less good compared to the possibility of catching Covid.
Well then the fourth dose, which in Italy is offered with the updated bivalents. More good news in the history of the evolution of the virus, that also the new subvariants they don’t seem to be any more lethal of the earliest forms of Omicron.
December 2, 2022 (change December 2, 2022 | 08:57)
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