It is circulating more and more, it is a fact.
But in what proportion?
Difficult to say very precisely.
The Delta variant of SARS-CoV-2, 40 to 60% more transmissible than the largely majority one (Alpha), is however the main element to follow in the coming weeks.
Given the very clear improvement in the health situation everywhere in metropolitan France, it seems to be the only one capable of partly spoiling the summer for some of the French.
In England, faced with a resumption of the epidemic with a Delta variant largely in the majority among the contaminations, the last stage of deconfinement has just been postponed by one month.
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The most responsive technique for measuring its spread is screening for positive tests.
Usually within a few hours, it is possible to tell which mutation a positive sample is identified with.
The new method, deployed throughout the country since June 14, targets in particular the L452R mutation, which the Delta variant sports.
5.6% of the positive tests screened last week were identified this way last week, according to data from Public Health France as of June 17.
Tuesday morning, Olivier Véran had mentioned to him “2 to 4% of screened tests” corresponding to the Delta variant, referring to the first unconsolidated figures.
Only 38% of positive tests screened
However, we cannot deduce that 2, 4 or 5.6% of positive cases are from Delta. Other variants, even if they are less present in France, also have the L452R mutation. “Today, we are not able to accurately estimate the share of the Delta variant with these data, work is underway to be able to do so. But we can say that a large majority [of the variants detected with L452R], at least two thirds, are of the Delta variant, ”replied Sibylle Bernard-Stoecklin, from the infectious diseases department of Public Health France.
Moreover, these first data are "to be interpreted with caution", warns the health agency in its epidemiological update published Thursday evening. Only 38% of the positive tests were screened and the mutations in question "are not yet systematically sought in all the tests screened, due to the progressive equipment of these new screening kits by the medical analysis laboratories" .
"It is useful for contact-tracing by considering by default that all these positive tests are Delta, but it remains vague", notes the virologist at the University of Montpellier Yannick Simonin, who heads a research group on viruses emerging.
In several territories, clusters linked to viruses bearing L452R have been identified.
The Delta variant would already represent 30% of confirmed or probable cases in the Landes.
Each time, the authorities launch an “action plan” and reinforce screening, tracing, vaccination and sequencing, the only technique that really makes it possible to identify a variant.
We are therefore forced, in the immediate future, to speak of “probable” clusters of Delta variant.
Limited sequencing
Sequencing consists of analyzing the complete genomic sequence of a virus.
During the last Flash survey conducted on May 25, 1% of the 1,723 sequenced samples corresponded to the Delta variant, against 0.2% two weeks earlier.
These results therefore date back to a month ago, i.e. a very long period while the epidemic is constantly evolving.
Activity continues apart from these bi-weekly Flash surveys (operations targeted on clusters, on travelers, etc.) but it is limited, with around 3,500 tests sequenced per week.
"It would take 10,000 to really know what is the share of the Delta variant", thunders the geneticist Philippe Froguel, very virulent against the French strategy.
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Public health France promises for its part a "rise" of the device in the coming weeks. “Given the drop in the number of cases, we should have much faster and more exhaustive sequencing in the weeks to come,” anticipates Yannick Simonin. The number of sequences published on the international Gisaid platform, which allows a detailed analysis of the situation in the different countries, is also limited (2,778 last week). "The deposits on Gisaid of sequences produced in France still need to be encouraged", underlines the Scientific Council.