Everything we know so far about the ‘Mu’ Covid-19 variant

WHO adds strain first discovered in Colombia to list of ‘variants of concern’

A health worker takes the temperature of a patient in Bogota, Colombia
A health worker takes the temperature of a patient in Bogota, Colombia
(Image credit: Guillermo Legaria/Getty Images)

A new Covid-19 strain, named “Mu”, has been added to the World Health Organization’s (WHO) list of “variants of concern”.

First identified in Colombia, Mu, or B.1.621, has been reported across South America, with an increasing number of infections appearing in Europe.

The WHO’s bulletin said the strain may be more resistant to vaccines, adding that “since its first identification in Colombia… 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”.

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Bad ‘Mu’ rising

According to the WHO’s weekly bulletin “global prevalence of the Mu variant among sequenced cases has declined and is currently below 0.1%”, however, “the prevalence in Colombia (39%) and Ecuador (13%) has consistently increased”.

It added that “the epidemiology of the Mu variant in South America, particularly with the co-circulation of the Delta variant, will be monitored for changes”. Latest government figures show there have been at least 48 confirmed cases of the new strain in the UK.

France 24 said there is “widespread concern over the emergence of new virus mutations as infection rates are ticking up globally again”. Cases of the Delta strain are again rising “among the unvaccinated and in regions where anti-virus measures have been relaxed”.

The Mu variant was first traced in Colombia in January and “may be able to evade antibodies generated from both prior infection and coronavirus vaccines at levels similar to that seen for the Beta variant”, The Telegraph said. However, this finding still “needs to be confirmed in further studies”.

Dr Julian Tang, a clinical virologist at the University of Leicester, told the paper that the variant shared three mutations with the Alpha and Beta strains, adding: “We know that these [spike] protein mutations give rise to some degree of vaccine escape and increased transmissibility.

“[Mu] also has mutations in other parts of the virus genome that may make it behave slightly differently from the other variants – but lab and real-world studies will be needed to fully characterise the impact of this variant on current vaccine programmes, clinical severity and transmissibility.”

Listing it as a variant of concern means the WHO considers it a strain that requires “special monitoring”, the Daily Mirror said. But “it is currently viewed as less troubling than the Delta and Alpha strains, which have been classified as variants of concern”.

‘Blink of an eye’

The emergence of a new strain has come “amid mounting concerns that low global vaccination rates and high transmission rates pose a perfect window for the emergence of new variants”, The Telegraph said.

Professor Danny Altmann, an immunology expert at Imperial College London, told the paper that “it looks like there’s genuine cause for concern in US, Central America, South America”, adding that “as we saw with Delta, a potent variant can traverse the globe in the blink of an eye”.

“Mu looks potentially good at immune evasion. For my taste, it’s a stark reminder that this isn’t by any means over: on a planet of 4.4m plus new infections per week, there are new variants popping up all the time, and little reason to feel complacent.”

While all viruses mutate over time, “certain mutations can impact the properties of a virus and influence how easily it spreads, the severity of the disease it causes, and its resistance to vaccines, drugs and other countermeasures”, France 24 said.

The WHO has so far identified four variants of concern, including Alpha, which is present in 193 countries, and Delta, present in 170 countries.

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