The lineage B.1.621 variant, named ‘Mu’ after the twelfth letter of the Greek alphabet, was first detected in the South American country of Colombia in January 2021.
All viruses mutate or undergo certain changes over time, helping them to spread easily, escape our vaccines, medicines and survive.
There are several SARS-CoV-2 variants circulating globally.
* Eta (lineage B.1.525, documented in multiple countries from December 2020);
* Iota (lineage B.1.526, first documented in the United States in November 2020);
* Kappa (lineage B.1.617.1, first documented in India in October 2020); and
* Lambda (lineage C.37, the so-called Peru variant, which was first documented in that country in December 2020).
WHO places a SARS-CoV-2 variant in the VOI list if it is seen to have certain “genetic changes that are predicted or known to affect virus characteristics such as transmissibility, disease severity, immune escape, diagnostic or therapeutic escape”.
To be added to the VOI list, a variant must also be “identified to cause significant community transmission or multiple Covid-19 clusters in multiple countries”, and suggest “an emerging risk to global public health”.
More dangerous mutants are categorised as ‘Variants of Concern’ (VOC).
According to the WHO, a VOI can become a VOC if it is demonstrated to be associated with an increase in transmissibility or virulence, or with a “decrease in effectiveness of public health and social measures or available diagnostics, vaccines, and therapeutics”.
Currently, four variants of the coronavirus are designated as variants of concern. They are:
* Alpha (lineage B.1.1.7, the so-called ‘UK variant’), which was first detected in the United Kingdom in September 2020, and is now present in at least 193 countries around the world;
* Beta (lineage B.1.351, the so-called ‘South Africa variant’), the first samples of which were detected in South Africa in May 2020, and which has so far been reported from 141 countries;
* Gamma (lineage P.1, the so-called ‘Brazil variant’), which was first detected in Brazil in November 2020, and which has been reported in 91 countries;
* Delta (lineage B.1.617.2), the variant that was first reported in India in October 2020 and is now present in at least 170 countries. The highly transmissible Delta variant is now the dominant strain of the virus in India, and was responsible for the devastating second wave of Covid-19 in April-May this year.
So, what is the Mu variant of Covid-19?
According to the WHO’s Covid-19 weekly epidemiological update published on August 31, the Mu variant (which includes the descendant Pango lineage B.1.621.1; known as 21H in Nextstrain nomenclature) has “a constellation of mutations that indicate potential properties of immune escape”.
The WHO bulletin said that since being first identified in Colombia, a few cases and some larger outbreaks of the Mu variant have been reported from other countries in South America and in Europe.
As of Thursday (September 9), a total 5,599 sequences, including both B.1.621 and B.1.621.1, had been submitted by 47 countries to GISAID, the global research database on viruses.
The bulk of the submissions were from the United States (2,435) and Colombia (1,041), followed by Spain, Mexico, Chile, Ecuador, and Canada.
The variant has not been detected in India so far. It is also not present in Africa, Australia, and most of Asia. Globally, the cumulative prevalence of Mu is less than 0.5 per cent, according to outbreak.info, using GISAID data.
Mu variant of Covid-19: What we know about its transmissibility
A paper published last month in ‘Infection, Genetics and Evolution’ noted that the Mu variant has several substitutions affecting the spike protein and amino acid changes.
The mutations — E484K, N501Y, P681H, D614G — seen in the Mu variant have been reported in other VOIs and VOCs. These mutations are known to help the virus escape the body’s immune defences and increase transmissibility.
According to the European Centre for Disease Prevention and Control, the Mu variant also has other spike mutations of interest (R346K) which need further study.
So can existing vaccines not work against Mu?
There are very few studies on this. In a letter to the editor published in July in the Journal of Medical Virology, a group of researchers from Italy wrote that the Pfizer/BioNTech vaccine was able to neutralise the Mu variant, but its effectiveness was less compared to other variants.
But this was a very small lab study, and more extensive research is needed.
The WHO bulletin last month said “Preliminary data presented to the [WHO’s] Virus Evolution Working Group show a reduction in neutralization capacity of convalescent and vaccinee sera similar to that seen for the Beta variant”, but cautioned that “this needs to be confirmed by further studies”.
That said, the possibility of the virus mutating into new and potentially more dangerous variants is constant. Experts and public health agencies around the world have urged universal vaccination against the coronavirus as quickly as possible.
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An illustration of the novel coronavirus. (Representational) 
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