New COVID-19 variant of interest, named “Mu”


On 30 August 2021, the World Health Organization (WHO) designated variant B.1.621 as a variant of interest (VOI). It was given the WHO label "Mu," and includes the descendant Pango lineage B.1.621.1. This variant has mutations that indicate potential properties of immune escape. Preliminary data show a reduction in neutralization capacity of convalescent and vaccine sera similar to that seen for the Beta variant, but this needs to be confirmed by further studies. 

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. Although the global prevalence of the Mu variant among sequenced cases has declined and is currently below 0.1%, the prevalence in Colombia (39%) and Ecuador (13%) has consistently increased. The reported prevalence should be interpreted with due consideration of sequencing capacities and timeliness of sharing of sequences, both of which vary between countries. More studies are required to understand the phenotypic and clinical characteristics of this variant. The epidemiology of the Mu variant in South America, particularly with the co-circulation of the Delta variant, will be monitored for changes. 


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