According to Outbreak.Info, using data from GISAID – a system that tracks SARS-CoV-2 variants, as of September 4, 5,659 Mu variant sequences have been detected worldwide. Among them, 2,436 sequences were discovered in the US.
The Mu variant, first detected in Columbia in January, remains relatively rare in the US although each state and the District of Columbia has recorded at least one case of this variant. According to Outbreak.Info, the Mu variant is most common in the state of Alaska, accounting for 3-4% of cases.
The Mu variant also accounts for about 1% of Covid-19 cases in Hawaii, while prevalence in other states is at less than 1%. In the US Virgin Islands, the Mu variant accounts for about 3% of cases.
The World Health Organization (WHO) has classified Mu as a “variant of interest”, with some preliminary data indicating that it possesses properties that confer resistance to current vaccines. However, it remains unclear whether the Mu variant has the same potency as the highly virulent Delta variant. According to the US Centers for Disease Control and Prevention (CDC), Delta is by far the dominant variant in the US, accounting for more than 99% of all Covid-19 cases.
The Mu variant was detected in only 0.1% of all SARS-CoV-2 infections in the US. However, this percentage is likely to be higher because only a small fraction of virus samples are sequenced to detect variants. In the world, the prevalence of Mu variant infection is recorded at a low level.
Outside of the US, the Mu variant is most common in the British Virgin Islands, accounting for 21 of 33 cases. This variant is also relatively common in Columbia, accounting for about one-third of cases. To date, the Mu variant has been detected in at least 46 countries around the world. Meanwhile, WHO data shows that the Delta super-infectious variant has so far spread to at least 174 countries.
Although the Mu variant has raised concerns about high transmissibility and vaccine resistance, WHO officials emphasize that the Delta variant remains a much more pressing concern.
“In some countries, the prevalence of Mu variant infections is increasing. But in other countries, the prevalence of this variant has decreased. Meanwhile, in any country, the Delta variant is spreading very quickly. I think Delta is the variant that is most worrisome because its transmissibility has increased,” said Maria Van Kerkhove, WHO technical lead on Covid-19.