The Mu variant— which also has the scientific name B.1.621 — was first detected in Colombia in January, and has been announced just as the Delta variant finally appears to be peaking in the U.S.
Over 4,600 cases have been spotted since then, and it has spread to more than 40 countries.
Almost 2,000 cases of the variant have been detected in the United States.
The WHO’s weekly bulletin claimed its mutations suggest it may be more resistant to vaccines, as was the case with the South African ‘Beta’ variant.
There are fears it may be more infectious, too.
But the agency warned more studies would be needed to examine this further, with the WHO having now formally labelled Mu a ‘variant of interest’.
The WHO report said: ‘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 percent, the prevalence in Colombia (39 percent) and Ecuador (13 percent) has consistently increased.
‘The epidemiology of the Mu variant in South America, particularly with the co-circulation of the Delta variant, will be monitored for changes.’
The WHO currently lists four Covid variants of concern — Alpha, Beta, Gamma and the highly-transmissible Delta.
Mu is the fifth variant of interest and is being tracked alongside Eta, Iota, Kappa and Lambda.
Infectious disease epidemiologist at the WHO Maria van Kerkhove tweeted: ‘Circulation of Mu is down globally and it [makes up] less than 0.1 per cent of currently shared sequences of Mu, but this needs careful observation.’
‘Monitoring and assessment of variants is ongoing and critically important to understand the evolution of this virus, in fighting Covid and adapting strategies as needed.’
Its key mutations include E484K, which can help it escape antibodies and is also found on the Beta and Gamma variants.
It also has the N501Y, which could help it spread easier. This mutation is also present in Alpha.
The coronavirus, called SARS-CoV-2, is mutating all the time as a result of genetic errors when it multiplies. Most mutations are harmless.
But ones that make it able to spread quicker or to survive longer inside the human body are the ones that are likely to stick around.