"No one can say what will happen, but, if there is an emergence that could threaten our control over the epidemic, it is more likely that it comes from a lineage within Delta," said late. September the biologist Samuel Alizon, research director at the CNRS.
As we explained at the time, the Delta variant sublineages acquired one or more additional mutations.
The one perhaps the most watched today has been dubbed AY.4.2.
To be very precise, this is a subline of… AY.4 subline of the Delta variant.
Read alsoCovid-19: should we be worried about new mutations in the Delta variant?
Increasingly present in the United Kingdom, AY.4.2 has been - little - detected in France in recent weeks, according to Public Health France (SPF) and the National Reference Center (CNR) for viruses of respiratory infections of the 'Pastor Institute.
But it must be "followed closely", indicate those two organizations in a long note published Monday evening.
We take stock.
What are its characteristics ?
This variant AY.4.2 presents two additional mutations compared to the “original” version of Delta (B.1.617.2): Y145H and A222V.
The position where they are located on the Spike protein on the surface of the virus, the entry route for neutralizing anti-SARS-CoV-2 antibodies, may raise concerns about an impact on the effectiveness of vaccines.
But there is nothing to confirm this with regard to these two mutations, whether they are analyzed separately or jointly.
“A222V had a lot of success with other variants this summer, but the analyzes had led to the conclusion that it itself did not provide any particular gain.
One can however ask the question about a combination with other mutations of the Delta variant ”, explains to Parisian Etienne Simon-Lorière, head of the unit of evolutionary genomics of RNA viruses at the Pasteur Institute.
Why is he worried?
Internationally, AY.4.2 has been identified almost only in the United Kingdom (but not all states provide the same “sequencing” effort, ie tracking down the entire genome of viruses).
Boris Johnson's country was one of the first affected by the Delta variant, at the end of last spring - after India, where this virus appeared at the end of 2020. For several months, Delta has represented almost all cases positive across the Channel.
But in recent weeks, AY.4.2 is spreading more and more.
Its share has increased and now reaches nearly 10% of the contaminations identified.
This evolution suggests that AY.4.2 is even more transmissible than the original Delta ... which was already 50% more transmissible than the previous Alpha variant (called "British"), itself around 50% more contagious than the original strain.
Of how many ?
Around 17%, estimates the British health security agency in its latest report, published on October 22.
It's a slow burner 🔥
But Delta is already * so * transmissible, it's notable that AY.4.2 is increasing in that context
• Growth rate estimates: 17% advantage for AY.4.2 over Delta
• Household SAR: 12% (8% -16 %) more transmissible pic.twitter.com/gDM16iOdxY
- Meaghan Kill 👻🔪🎃☠️ (@kallmemeg) October 23, 2021
But be careful: we do not know, for the moment, whether this is explained by its characteristics or by the context in which it has spread (in highly affected areas, among children who are not vaccinated, etc.).
This 17% advantage “cannot be interpreted as a change in biological transmissibility”.
"A founding event can lead to the rapid diffusion of a variant in a population, in particular after one or more large clusters", point out for their part the French authorities.
Read also40,000 cases of Covid per day: why the United Kingdom is not doing it
At the same time, the number of new positive cases has risen sharply in recent weeks in the UK, reaching almost 50,000 per day.
The variant AY.4.2 may have contributed to it, but "nothing indicates that
(this)
increase is solely due to its diffusion", we read in the note published Monday evening on the site of Public Health France.
“It is only in the United Kingdom that we see this spread of AY.4.2, but it is also a country where the virus circulates enormously.
There are few restrictions, and that can allow a sub-lineage to be very successful, ”adds Etienne Simon-Lorière.
Does it circulate in France?
Yes. 19 suspicions of variant AY.4.2 were identified from August 30 to October 1. This number seems low, but keep in mind that not all positive cases are “sequenced” and that a characteristic mutation may not be detected in some viruses. “There could be a slight underestimation,” says Etienne Simon-Lorière. 16 of these 19 cases come from Île-de-France, but "the over-representation of this region should be interpreted with caution" given the small sample, warns SPF. "There is no indication at this stage that the cases are linked" and "at least" two of them were vaccinated.
To summarize, Public Health France and the National Reference Center speak of a "possible low noise circulation
(of the AY.4.2 variant)
, particularly in Île-de-France, but without a signal in favor of a significant diffusion at this Stadium ".
We see a similar situation in several of our neighbors, such as Germany and Denmark.
And the health authorities praise "the French genomic surveillance system" which "has demonstrated its ability to detect this variant, even though its presence in France is currently very low".