SARS-CoV-2 variant of interest, Mu (21H/B.1.621)

6 September 2021 

The World Health Organization (WHO) has recently (30 August 2021) classified the PANGO lineage B.1.621 (nextclade assignment: 21H) as a variant of interest (VOI) and assigned it the Greek name “Mu”. This variant was first detected in Colombia in January 2021 (Laiton-Donato, 2021, medRxiV).  It has since spread across North America, South America and Europe, with detections in Asia. The majority of the Mu sequences (5123) have been detected in North America (55%, n=2841) followed by South America (23%, n=1328), Europe (18%, n=948) and Asia (0.1%, n=6). To date (3 September 2021) there have been no cases of Mu detected on the African continent, including South Africa. Currently, it accounts for less than 1% of the globally circulating viruses with Delta accounting for 88%.

The Network for Genomic Surveillance in South Africa (NGS-SA), which includes the National Institute for Communicable Diseases (NICD), continuously and rigorously monitors SARS-CoV-2 sequences circulating in South Africa. This work is crucial in the early detection of SARS-CoV-2 variants, including Mu.

The Mu variant is defined by the following mutations within the spike protein: T95I, Y144S, Y145N, 146N insertion, R346K, E484K, N501Y, D614G, P681H and D950N. Many of these mutations (T95I, E484K, N501Y, D614G, P681H and D950) have been seen before in other VOIs or variants of concern (VOCs) including Beta and Delta. Some of these mutations have previously been associated with decreased antibody responses and increased transmissibility. This variant will likely, therefore, have similar properties to other variants with increased transmissibility and reduced sensitivity to antibodies in vaccines and those who have recovered from COVID-19.

Nevertheless, both vaccines that are currently being rolled out in South Africa have high levels of protection against severe disease requiring hospitalization and death even against VOI/VOCs such as Beta and Delta and therefore will likely also protect against Mu. In addition to vaccination, we know that non-pharmaceutical interventions such as the wearing of masks, sanitizing and washing your hands, keeping a safe distance and avoiding crowds are effective at preventing the spread of SARS-CoV-2 regardless of the variant.

Issued by NICD, 6 September 2021