It is scrutinized by experts around the world.
In the UK, Delta's subvariant 'AY4.2' is now considered a 'variant under investigation (VUI)' by the UK Health Safety Agency and is climbing by a step in the English classification, which ranks the variants according to their dangerousness.
"Preliminary elements seem to prove that it has a higher transmission rate compared to the Delta", explained the British Public Health Agency, to justify this decision, taken on October 20, but unveiled this Friday.
Thus, the English authorities will redouble their efforts to sequence and study the AY4.2 variant.
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Indeed, the British authorities consider that the progression of this form of Sars-Cov-2, very close to the Delta variant, but with a few different mutations, justifies reinforced monitoring by scientists.
Until now, this strain was still monitored, but classified a step below "VUI".
From 2% to now 6% of analyzes
AY4.2 went from less than 2% of screenings analyzed in July to more than 6% in October.
If it proliferates, this is potentially a sign that it has an advantage over other variants in circulation.
"It's worth keeping an eye on him," epidemiologist François Balloux said on Twitter last week.
“Its recent increase would be consistent with a ~ 10% transferability advantage.
Although, based on its genetic makeup, it is not a priori an obvious candidate for VOC, ”he then summarized, VOC being the highest classification (Variant of concern).
However, the progression of AY4.2 may be the result of other factors than its inherent contagiousness.
"More evidence is needed to determine if this is related to a change in the behavior of the virus or to epidemiological conditions," the Public Health Agency said on Friday.
Thus, being investigated does not mean "more contagious" or "more dangerous", but there is still a risk, which scientists are trying to measure.
The effectiveness of vaccines not questioned
"No one can say that there is evidence to say that this virus is different, that is to say more severe, more transmissible, or evading the vaccine response differently," he said. morning during a press point Sibylle Bernard-Stoecklin, epidemiologist at Public Health France.
An in-depth analysis of this subline and its characteristics is currently being carried out in France.
For its part, the WHO did not include AY4.2 in the “VOI”, the equivalent of the British “VUI” classification, precisely because of the lack of a sufficient number of data.
This variant "does not seem to cause a more serious version of the disease or to make the vaccines currently distributed less effective", the British Agency nevertheless stressed on Friday.
That it is from the Delta variant does not necessarily mean that it is more dangerous than a form of Sars-Cov-2.
Each line of Sars-Cov-2 accumulates an average of two mutations per month.
Delta now has 45 sublines.
If AY4.2 is so closely watched, it is also because of the Anglo-Saxon context.
The epidemic is progressing again in the United Kingdom, which on Thursday recorded more than 50,000 new cases tested positive, for the first time since July.
The number of hospital admissions is up about 19% from last week's toll.