This variant was discovered in January 2021 in Colombia, the Mu variant is now dominant in this country and is becoming established in the world. It has been recognized, at the end of August, as a “variant to follow” by the WHO.
Could Mu be the new Delta? Discovered for the first time in January in Colombia, the new variant of the coronavirus, named Mu or B.1.621, is worrying. In this South American country, it is now predominant and is at the origin of the most deadly wave of the pandemic last spring, health authorities said Thursday.
“More or less 60% of the deaths that we have sequenced are of this lineage,” explained on a local radio an official of the National Institute of Health, Marcela Mercado. Infections and deaths reached a record level between April and June 2021, with up to 700 deaths per day, and a hospital system on the verge of collapse.
In late August, it was classified as a “variant to watch” by the World Health Organization (WHO). Here is what is known about variant B.1.621, according to scientific nomenclature.
The global presence of this variant among sequenced cases is currently less than 0.1%, but it has “steadily increased” in Colombia and Ecuador, where it is now responsible for about 39% and 13% of infections, respectively, WHO reports. As of August 29, 4,500 sequences had been deposited on GISAID, a reference platform where data shared by laboratories studying genomes are listed, says on Twitter the director of the Covid-19 technical team at WHO, Maria Van Kerkhove.
In total, recalls Marcela Mercado of the Colombian National Institute of Health, Mu has already been identified “in more than 43 countries” in South America, but also in Europe. In France, the Mu variant appeared for the first time in May 2021. It has since been detected 105 times, without successfully taking hold, according to data from Santé Publique France (SPF), which notes that its level of circulation remains very low overall. Its prevalence rate is currently 0.3% or less, SPF says, noting that the mutation has not been spotted in the last two Flash sequencing surveys, which are conducted weekly on a sample of positive samples.
“At present it is not known how B.1.621 will behave in relation to Delta and this variant is being carefully monitored, although increased transmission in relation to Delta seems unlikely,” Santé Publique France further notes. For the health authorities, Mu “does not appear to have characteristics that give it a competitive advantage over Delta” and thus may never become dominant. “No data on severity are available at this time,” they added.
Mu is the fifth “variant of interest” to be monitored by WHO since March. It has a number of mutations that suggest it may be more resistant to vaccines, the UN agency warns. Preliminary data from Public Health England show reduced vaccine efficacy “similar to that observed for the Beta variant” originally identified in South Africa, WHO said. Messenger RNA vaccines remain 77% effective against the Beta variant. However, further research is needed to confirm possible vaccine resistance.
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