The Mu Covid-19 variant: What is it and why does WHO list it as ‘variant of interest’?

The Mu variant, also known scientifically as B1621, was first identified in Colombia in January this year. PHOTO: AFP

A new coronavirus variant known as Mu, first identified in Colombia in January, is being closely monitored.

About 4,500 cases of the Mu variant have been reported across the globe, with more than half of them discovered in the United States. It has also been reported in other South American countries, Europe, Japan and Hong Kong.

Here is more information on the variant:

What is it?

The World Health Organisation (WHO) on Aug 30 added the Mu variant - known by scientists as B1621 - to the list of "variants of interest" because of preliminary evidence that it can evade antibodies.

The Mu variant has a "constellation of mutations that indicate potential properties of immune escape", noted a WHO weekly update published on Aug 31.

All viruses, including SARS-CoV-2 which causes Covid-19, mutate over time and most changes have little or no effect on the properties of the virus. But certain mutations can alter how easily a virus spreads, the severity of the disease it causes, or its resistance to vaccines and drugs.

Where has it emerged?

It is now Colombia's predominant strain and behind its deadliest pandemic wave yet, health official Marcela Mercado said on Sept 2.

The variant was responsible for Colombia's deadly third infection wave between April and June. During this period, with about 700 deaths per day, nearly two-thirds of tests from people who died came back positive for the Mu variant, she said.

The Mu variant, already in more than 43 countries and areas, has shown high contagiousness.

Japan on Sept 1 confirmed its first cases of the Mu variant in two travellers from Britain and the United Arab Emirates, reported The Japan Times.

In Hong Kong, health authorities said on Sept 3 that three people have been found to be carrying the Mu variant when they arrived in the city in recent months. Two of the patients had flown in from Colombia and were confirmed infected in early June, while the third arrived from the US. She was confirmed infected in July.

What is a variant of interest?

The WHO's variant of interest (VOI) designation suggests that the strain has genetic changes that may affect virus characteristics, such as increased transmissibility, disease severity, immune escape, diagnostic or therapeutic escape. VOIs have also been identified to cause significant community transmission or multiple Covid-19 clusters in multiple countries. Other VOIs named by the WHO include Eta, Iota, Kappa and Lambda.

The WHO also lists four coronavirus variants of concern (VOCs): Delta, Alpha, Beta and Gamma.

Is the variant more contagious? How does it fare against existing vaccines?

Preliminary data shows that Mu may more easily evade vaccine protection, similar to that seen for the Beta variant, first discovered in South Africa.

According to the Guardian, a risk assessment released by Public Health England last month suggests the Mu variant is at least as resistant as the Beta variant to immunity, but is unlikely to become more transmissible than the Delta variant.

However, further studies are needed to know more about the Mu variant's characteristics and the WHO update noted that Mu's epidemiology will be monitored for changes.

A study in The Lancet Infectious Diseases on Aug 13 suggests that the Mu variant has "two cases of a potential vaccine escape" and noted that several of the spike mutations within Mu "have been reported to show reduced neutralisation by antibodies".

It added that the strain's presence of mutations associated with vaccine escape may warrant a reclassification of Mu to a variant of concern.

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