Mu, or B.1.621, was first identified in Colombia and cases have since been recorded in 38 other countries, predominantly in South America and Europe.
“Since its first identification in Colombia in January 2021, there have been a few sporadic reports of cases of the Mu variant, and some larger outbreaks have been reported from other countries in South America and in Europe,” a weekly epidemiological update released by WHO on August 31 read.
Over 4,500 sequences (3794 sequences of B.1.621 and 856 sequences of B.1.621.1) have been recorded in 39 countries as of August 29, the report said, citing information uploaded to the GISAID Initiative, a global science initiative that provides open-access to genomic data of influenza viruses.
Although the global prevalence of the Mu variant has declined and is “currently below 0.1 percent” the prevalence in Colombia (39 percent) and Ecuador (13 percent) has “consistently increased,” the report reads.
The health body also notes that the variant “has a constellation of mutations that indicate potential properties of immune escape,” adding that more studies are needed to understand the phenotypic and clinical characteristics of the variant.
“The epidemiology of the Mu variant in South America, particularly with the co-circulation of the Delta variant, will be monitored for changes,” the report notes.
The variant is listed as one of five “of interest” by the WHO, including Eta, Iota, Kappa and Lambda.
Four other variants “of concern” and considered as having potential to make the pandemic worse are listed as the Alpha variant (first recorded in England and seen in 193 countries), the Beta variant (now seen in 141 countries), Gamma in 91 and Delta in 170 countries.
There are currently more cases of the Mu variant recorded in the U.S. (2,065) than any other country, according to a country submission count tabulated by GISAID. This figure is followed by 852 cases recorded in Colombia and 473 in Spain.
Another variant of COVID-19, known as the C.1.2, is also causing concern among scientists because it is more transmissible and resistant to vaccines than other variants of the virus.
A pre-print study that emerged last week said the variant, which was first detected in South Africa in May, has since been found in Botswana, China, Democratic Republic of the Congo, the United Kingdom, Mauritius, New Zealand, Portugal and Switzerland.
The newly-discovered variant seems to have an unusually high mutation rate and more mutations of other variants of concern (VOCs), the study, led by a team of South African scientists, noted.
It also noted that it is more likely to cause severe COVID-19 than other variants.