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mu variant

How much do we know about the Mu strain of Covid-19, the WHO's latest 'variant of interest'?

Four cases of this variant have been identified so far in Ireland, according to latest figures.

EARLIER THIS WEEK, the World Health Organization (WHO) announced that it is monitoring a new coronavirus variant called ‘Mu’. 

Known as B.1.621, the variant was first identified in Colombia and initial evidence shows it has some similar traits to the Alpha variant, first identified in the UK last year, and the Beta variant, first seen in South Africa.

The WHO has classified the strain as a ‘variant of interest’, which was once the same designation given to the now-dominant Delta variant.

So just how concerned should we be about Mu?

All about Mu

The Mu variant is a mutation of the SARS-CoV-2 coronavirus which causes the illness known as Covid-19.

The variant was first identified in Colombia in January this year. It has since been reported in other South American countries and in Europe. 

The WHO said its prevalence around the world has declined recently, accounting for just 0.1% of cases. 

In Colombia, however, the strain accounts for 39% of cases, while it also makes up around 13% of cases in Ecuador. 

The Health Protection Surveillance Centre (HSPC) has said that four cases of the Mu variant have been identified in Ireland as of 21 August.

In the UK, data shows that 48 cases of the variant have been identified there up to 25 August.

The variant has mutations that indicate a risk of resistance to vaccines, the WHO said, adding that further studies were needed to better understand it.

“The Mu variant has a constellation of mutations that indicate potential properties of immune escape,” the WHO’s weekly pandemic bulletin said on Tuesday.

The European Centre for Disease Prevention and Control (ECDC) also said there’s evidence Mu impacts on transmissibility and immunity.

This means it could impact the spread of the virus and protection against the disease, typically acquired through vaccination. 

There is no evidence so far that this variant is more severe than others. The ECDC said transmission in Europe has been sporadic and related to travel. 

Delta buffer

All viruses, including the SARS-CoV-2 coronavirus, adapt over time but most mutations have little or no effect on the properties of the virus.

But certain changes 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.

The WHO said it routinely assesses whether coronavirus variants alter transmission or disease characteristics or other changes such as impact on vaccine protection. 

This is a crucial step for scientists and public health officials, but there are questions about whether this is something the average person needs to be concerned about.

Dr Gerald Barry, assistant professor of virology at University College Dublin (UCD), said it appears at the moment that ”nothing jumps out” to definitively say Mu is “worse than Delta or more transmissible”.  

“Delta is almost acting as a buffer to other variants,” he told The Journal.  

Barry explains that the Delta strain is “so fit in the sense that it seems to be more transmissible and dominant to other variants” that it will take something “much more transmissible” to overtake it.

It’s interesting from a scientific point of view, but at the moment in terms of the general public it’s not something people need to be concerned about.

“If ever a variant pops up showing stronger resistance, then yes it’s something to pay attention to and may become an issue in the country,” he said. 

A variant that is “more able to move between vaccinated people [has] the potential in a highly vaccinated population to become a problem”. 

Dr Barry added: “Unless it’s something that’s going to change our current trajectory, it’s not going to change how people live their lives currently.

“Let science keep an eye on it but be aware that if anything changes, the general public will be very aware of it.”

Previously seen mutations

The Mu variant has a mixture of mutations seen in the Alpha and Beta variants and some unclear variations, hence the need for further sequencing and analysis to gain a better understanding about it. 

“This is now another variant that has developed independently the same kind of mutations as other variants,” Dr Barry said.

This is known as ‘convergent evolution’, whereby the virus is adapting with the same mutations in different parts of the world.

“The virus is still adapting to humans and finding a common way every time to become better at infecting humans,” the virologist said. 

“This is a natural thing that’s going to happen with any virus that comes into a population.” 

He said there is reason for optimism as 18 months into the pandemic, scientists are seeing the “same mutations keep popping up” in different variants.

“Delta has some unique things and some common things, but even that advantage is not fully understood,” Dr Barry said. 

Classifying variants

The WHO said the Mu variant has a “constellation of mutations” that indicate potential properties of immune escape. 

It added that more studies are needed to understand the characteristics of this variant. 

The epidemiology of the variant, especially in circulation with Delta, will be monitored for changes, the WHO said. 

The WHO currently identifies four SARS-CoV-2 variants of concern – Alpha (UK), Beta (South Africa), Gamma (Brazil) and Delta (India). 

A variant of interest is a coronavirus variant with changes predicted or known to impact virus characteristics such as transmissibility, disease severity and immunity.

These variants are also identified to cause “significant community transmission or multiple Covid-19 clusters” in several countries with increasing relative prevalence and increasing case numbers, or other epidemiological impacts to indicate an emerging risk to public health. 

A variant of concern is a variant of interest that is associated with one of more of these changes: 

  • Increase in transmissibility or “detrimental change” in epidemiology
  • Increase in virulence or change in clinical disease presentation
  • Decrease in effectiveness of health and social measures, or available drugs and vaccines.

However, it will likely take much more research and time before the Mu variant gets to this point, if that is to happen at all.

Additional reporting by AFP.

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