Omicron variant, Silvestri: “Here’s what we know and what can happen”

It is different from Delta, more transmissible but less capable of infecting the lung, with milder symptoms and could cause less severe disease. These are some of the features of the Omicron variant of Sars-CoV-2 that have emerged so far. To list them is the virologist Guido Silvestri, a professor at Emory University in Atlanta in a long post on Facebook in which he explains that he tried to “put some order on the tumultuous discoveries of recent days on Omicron”, “while the virologists ‘zero-tituli on Twitter are competing to see who shoots the biggest “. The expert takes stock of what we know so far, what future scenarios could be, but also what we can do.

A recipe the latter in 5 points. First of all for Silvestri, the “temptation to think of controlling this virus with methods based on imposing forced separation between people to the bitter end must be avoided. Methods that have already proved scarcely useless and certainly unsustainable against the previous variants but also against Omicron itself ( see Australia and Holland for two recent examples) “. Second: “Pushing hard for universal vaccination, including third doses (which give much greater neutralizing protection against Omicron than two doses), and especially including vaccination of children, including those under 5 years of age as soon as possible. ”

The list continues with the therapies: “Try to implement antivirals as soon as possible, in particular paxlovid “, Pfizer’s anti-Covid pill” andmonoclonal antibody Sotrovimab, which are effective against Omicron, using them in a widespread way in all infected subjects ‘at risk’ “. And again: enhance the health service, and promote” factual, science-based, neither catastrophic nor minimizing “communication.

Omicron is different from Delta and the other variants of Sars-CoV-2, with 45 amino-acidic mutations compared to the Wuhan strain, of which 30 in the Spike protein and 15 in the Receptor Binding Domain (Rbd), the part of Spike that is binds to the ACE2 receptor. It is “replacing almost everywhere in the world” the Delta. “This increased transmission appears to be linked to a high affinity for the Ace2 receptor and the ability to bypass antibody immune responses (and perhaps a better ability to survive in aerosols),” explains Silvestri.

The new mutant is “clearly less pathogenic than Delta in the experimental animal and appears to cause less severe disease in humans, with a reduction in the risk of hospitalization currently estimated at between 67-80% “. Omicron also contains” an interesting and poorly characterized mutation in a protein that could affect the mutagenic capacity of the virus “, notes the expert who suggests 3 possible scenarios.

The “best one is that Omicron spreads by remaining as such or perhaps further refining its ability to give an upper respiratory infection (the so-called” cooling “, which some have already speculated). In this case the surge could be very high as numbers of infections, but also rather rapid in time (see Gauteng), and with lower lethality than the previous waves “.

The intermediate scenario “is that Omicron, despite the reduced lethality, eventually causes a significant absolute mortality in non-vaccinated or otherwise immune subjects, especially if elderly or suffering from comorbidities, simply as a consequence of the large number of infections”.

The worst case scenario, he concludes, “is for Omicron to ‘backtrack’ on the three ‘favorable’ mutations and then return to being effective at infecting the lung without losing its increased transmissibility. The likelihood of this scenario is quite low, too. because I cannot imagine a reason why this variant should acquire a clear evolutionary advantage over the previous one. However, this possibility is by no means impossible, and deserves adequate preparation at the level of vaccines “.