He now has a small name, joining Eta, Iota, Kappa and Lambda.
“Mu” is now one of the variants of Covid-19 “to follow”, according to the official name of the World Health Organization (WHO).
Spotted in January in Colombia, it has since spread to Latin America and, in smaller proportions, elsewhere in the world.
If he is particularly worried, despite a low prevalence, it is because he could resist the vaccine.
What is the "Mu" variant?
This variant was, until Wednesday, better known under the name of “Colombian variant”, when we did not use its scientific name, B.1.621.
Discovered in the South American country at the beginning of the year, it includes several changes, including three particularly scrutinized: E484K, N501Y and P681H.
These are alterations that are found in other variants such as Beta or Gamma (for the N501Y and E484K mutations) or Alpha (P681H).
And besides, why "Mu"?
It is actually the 12th letter of the Greek alphabet.
Since June, the WHO has decided to no longer use the geographical origin of variants to name them so as not to stigmatize these countries, preferring to choose letters of the Greek alphabet to name them, according to their order of appearance.
So the British variant became Alpha, South African Beta, etc.
Should we be worried?
The Mu variant has "a constellation of mutations which indicate a potential for immune evasion," explains the WHO in its weekly report. In other words, the vaccine could work less on B.1.621. However, the first data, continues the WHO, suggests that the effectiveness of the vaccine on Mu is "similar" to that on Beta. A study by the British health agency came to the same conclusions in early August. Another, published in mid-July in the Lancet Regional Health Europe, notes that the two doses of an mRNA vaccine (Pfizer and Moderna) confer 77% protection against the beta variant.
The question of the effectiveness of the vaccine on the Colombian variant had already arisen in August.
Seven residents of a Belgian retirement home, all vaccinated, died within two weeks of being infected with this variant.
However, there is nothing to say that the Mu variant is more "dangerous" than another, from a symptom point of view.
The British health agency also suggested similar transmission of the B.1.621 variant and Alpha.
What to expect
Will Mu join Alpha, Beta, Gamma and Delta, the variants that circulate the most in the world - with Delta largely in the lead, since its appearance in India? We are far from it: it would correspond to less than 0.1% of positive cases. In Colombia, where it appeared, and in Ecuador, the Mu variant represents respectively 39% and 13% of cases. But, notes the WHO, its share has "steadily increased". This is why the agency, which specifies that not all countries have the same testing and sequencing capacities, has placed this variant in the list.
According to the international database Gisaid, the Mu variant has been detected in around 40 countries, including the United States, Mexico, Spain, the Netherlands and Italy. France has also detected it "sporadically" in metropolitan France since May, specifies Public Health France (SPF), in a recent inventory of variants. "At the moment we do not know how B.1.621 will behave in relation to Delta and this variant is the subject of careful monitoring, even if increased transmission compared to Delta seems unlikely", wants to reassure the agency.