DECRYPTION – Since June 2021, the World Health Organization (WHO) has been using Greek letters to designate the main lineages of Covid-19. However, this is not the case for the latest variants in circulation.
“BQ.1.1” in France“BF.7” in China“XBB.1.5” to United States… The different names of the variants of Covid-19 currently circulating in the world are confusing. “We should use names that are more suitable for the public»suggested about this in Le Figaro Mircea Sofonea, epidemiologist and lecturer in the PCCEI unit of the University of Montpellier, then questioned on the “XBB.1.5” subvariant growing in the United States. Why does the scientific community choose such an obscure nomenclature for laymen?
These variants, like all those currently circulating, “descend from the Omicron variant», first remind the Figaro Florence Débarre, researcher in evolutionary biology at the CNRS.
Use of the Greek alphabet
To understand the non-attribution of Greek letters to current strains, we must go back to the beginning of the pandemic. Originally, variants were named according to where they were detected (“English variant», «South African variant», «Brazilian variant», …). On May 31, 2021, the World Health Organization (WHO) announced that it would now use Greek letters to designate the variants of Covid-19. The goal was to have nameseasy to pronounce and remember“, but also to prevent the general public and the media from using names “stigmatizing and discriminatory” referring to the place where the first cases of variants were detected, had explained the WHO.
A new Greek letter is assigned to each new variant judged to be of concern and sufficiently different from the variants in circulation (Alpha, Beta, Delta, Omicron, etc.). On his sitethe WHO defines a variant of concern as a variant “associated with one or more changes, which are of global public health significance». The WHO lists three changes as follows:increased transmissibility», “increased virulence” and “reduced effectiveness of public health and social measures».
Regarding the current sub-variants, the answer remains the same. The WHO tells the Figaro that“a new label, i.e. a new assignment of a variant of concern, would be given if there was a variant that was sufficiently different in its impact on public health, and which would require a change in the public health response .” Which is currently not the case.
“Currently we remain in the Omicron dynastyinsists Florence Débarre. BA.2 and BQ.1.1 [respectivement responsables de la sixième et de la neuvième vague en France, NDLR] have similar properties». Contrary to Delta and Omicron which do not have the same characteristics. Omicron took over from Delta at the end of December 2021. “Delta and Omicron do not come from the same branch of the family tree, they are clearly different», supports Florence Débarre. Even if all the variants of Covid-19 have the same original strain of the virus as “common ancestor».
A family tree
So where do the letters and numbers used today come from? From the Pango systemset up in 2020 by a group of British researchers and used by scientists even before Greek letters were used for Covid. “The fundamental principle is that the names of the lines represent the ancestry and the descent”explained in June 2021 to National Geographic Oliver Pybus, an evolutionary biologist at Oxford University, who helped design Pango. The latter can be read as a family tree of Covid-19. Each branch corresponds to a line. “This makes it possible to trace the different generations of virus lineages», justifies Florence Débarre.
Pango lines work with a letter, followed by numbers. A dot separates the letters from the numbers and the numbers from each other. Originally, there were two main lines of Covid-19, named “A” and “B”. Only variants from the “B” line are circulating today. Thus, “B.1” descends from “B”. “B.1.1.1” comes from “B.1.1”, which itself comes from “B.1”. Following this same logic, “BA.1”, the first Omicron variant which replaced “Delta” at the end of 2021, is a cousin of “BA.2” or even of “BA.5”, responsible for the seventh and eighth waves in France .
Pango lines cannot have more than three points. If too many digits were to be added, a new letter would replace them. For example, the original name of “BQ.1.1”, which therefore descends from “BQ.1”, is “B.1.1.5220.127.116.11.18.104.22.168.1.1”. Note that “BQ.1.1” comes from the line of “BA.5”. “B.1.1.529” corresponds to the real name of the first Omicron variant. The new letters are given in alphabetical order, according to the date of appearance of the sub-variants.
The X in “XBB” is used to designate recombinants, those variants resulting from the combination of two strains such as “XBB.1.5”. “XBB.1.5” therefore comes from the line of “XBB.1”, but “it has a key mutation that the parent line did not have, explains Florence Débarre. Similarly, a new lineage arises when multiple mutations occur, or when a single mutation is large enough.
If the virus changes completely, the first letter may also change. The gamma variant, detected for the first time in Brazil, was thus called P.1, although it descended from “B.1.1.28” and its name could therefore have been “B.22.214.171.124”.
This Pango system serves as a common language for all scientists. To promote understanding by all, some scientists use the names of mythological creatures on social networks. “BQ.1.1” was thus nicknamed “Cerberus– three-headed dog guarding the gate of the Underworld, “BF.7” “Minotaur– half-man, half-bull creature – and “XBB.1.5” “kraken– sea monster with multiple tentacles. “Mythological appellations have been around for a long time, it’s not new», comments Mircea Sofonea.
However, these new names are not unanimous. “These names have no scientific basis, they were invented on Twitter“, reacts Florence Débarre. “What bothers me is that they are mythological monsters, which can alarm unnecessarily” the general public, she laments.
In September 2021, the WHO had said consider using constellation names for future variants. Without going any further.
SEE ALSO – Covid-19: should we be concerned about the BQ 1.1 variant?