Covid-19, how the new variants are evolving

The first signs of “convergent evolution”Of the variants of Sars-CoV-2. That is, there seems to be none at the moment variant of Covid-19 which is taking over another, as in the past, but which are rather circulating different subvariants which accumulate very similar mutations, all associated with a major immunoresistance of the virus.

It is a mechanism that scientists do they defined evolutionary convergenceborrowing the name given to the phenomenon whereby different species living in the same type of environment, under the pressure of the same environmental pressures, evolve by developing structures or adaptations that lead them to closely resemble each other.

What happened in the past two years

It must be said that the oddities haven’t started now. The evolution of Covid-19 was bizarre right from the start. In the second half of 2020, after an initial period in which the virus has changed very little, the three variants emerged Alpha, Beta And Range: three different strains in three different parts of the world, all with relatively similar mutations. In 2021 the scenario has changed: in the world, several waves have begun to be registered, each dominated by a variant, with the scepter passed from Alpha to Delta and then from Delta a Omicron; in this case, however, each variant was significantly different from the one that preceded it. In short, one was no longer in a regime of “continuous” evolutionin which a single strain progressively accumulates mutations, but rather in an almost regime discreetmade of great evolutionary leaps, each related to a strain that almost seems to come out of nowhere. Finally, between the end of 2021 and the beginning of 2022 it seems that the situation has returned to the previous regime, with the diffusion of the sub-variants BA.1, BA.2, BA.3, BA.4 and BA.5 and their second generations, which all appear to have very similar forms in terms of mutations.

The present and the future: is Centaurus coming?

At this time, after the increase in infections a few months ago due to the Omicron variant 5 (currently the most widespread and responsible, in the United States80% of cases), and after a relatively “quiet” summer, the attention of experts is focused on a possible one autumn wave: according to the authors of one study Italian published on European Journal of Internal Medicinethe autumn wave could be dominated by an Indian variant, the so-called Centaurus , a second generation evolution of the Omicron BA.2 variant, codenamed BA2.75. It is apparently a very efficient variant in binding to human Ace2 receptors, which would potentially make it able to spread very quickly.

Homoplasia and evolutionary convergence: birds and bats

Thus we come to the theme of evolutionary convergencerecently addressed by New Atlas in a piece on the theme of the future of Sars-CoV-2 which put together the latest considerations of several virologists on the issue. This is not a new topic: already in June 2020, for example, a study published in the journal Infection, Genetics and Evolution by a group of researchers led by Francois Bellouxfrom the Institute of Genetics at University College London, had suggested that the evolution of Sars-CoV-2 in different parts of the world was characterized by high levels of homoplasia – that is, he was adapting to the human being in a similar way. Analyzing nearly 8 thousand Sars-CoV-2 sequences from countries of different geographic areas, the authors of the work had observed at least 198 mutations that emerged independently. “The phenomenon referred to in this work – he had commented to theAgi Giuseppe Novelligeneticist atTor Vergata University From Rome – is well known, it is about ‘evolutionary convergence’ and it is a common behavior among viruses. Homoplasia essentially concerns the fact that in evolution some biologically different structures, such as the wings of mammals, such as bats, and the wings of birds, achieve the same purpose even if they come genetically from different conditions. Homoplasia is therefore a sort of evolutionary convergence of a different biological origin “. In evolutionary biology, in short, the theory of evolutionary convergence explains how and why completely different organisms can evolve, separately but under the pressure of the same environmental pressures, similar traits.

To each his own spike

In the case of SARS-CoV-2the same concept applies to the structure of the now famous protein spike: the Rbdor receptor binding domainwhich is located on the top of the spike and helps the virus to attach itself to certain receptors in human cells, thus playing a fundamental role in the infection and replication of the pathogen. A study (still in pre-print on BiorXive) recently showed that all of Omicron’s new sub-variants feature mutations on Rbdwhich, according to experts, indicates that the virus is looking for (and finding) new strategies to evade human immunity. “The convergent evolution of Rbd – has explained Yunlong Caoone of the authors of the work – it means that the Rbd mutations that have evolved from the more recent Omicron strains all converge towards the same sites. Observing such a pattern means that Sars-CoV-2 will evolve immuno-evasive mutations much more frequently than in the past, and that therefore the new mutations will be much more immuno-evasive.“.

Several other “variant hunters” arrived at the same results independently, so much so that the phenomenon was nicknamed The Great Convergence. What is still unclear, however, is how much there is to worry about: “It’s possible – says Cao again – that the cells of the immune system continue to recognize the virus despite these mutations in Rbd, since they also rely on other parts of the virus, not yet subject to mutations. But further evolutions could also occur that completely neutralize the efficacy of antibodies, cause high rates of infection and lead to severe disease in some individuals ”.