Following the devastating second wave of the COVID-19 pandemic in India, the world paid attention to a new variant of the coronavirus. Named Delta, it was blamed for the rapid surge in cases in April-May this year. Now, the World Health Organization (WHO) has said it was monitoring the spread of another variant of interest — Mu. It was first identified in Colombia in January and has since infected people in South America and Europe. Mu's possible resistance to vaccines is what makes it risky for the global population. Now, the WHO has said that more research was needed to better understand its behaviour.

With the latest addition, there are five variants of interest for the WHO — Eta, Iota, Kappa, Lambda, and Mu.

Mutations in viruses are not new. All viruses, including SARS-CoV-2, undergo change over time. Most of these changes are inconsequential, but some can alter properties to make these viruses more virulent or escape the treatment or vaccines.

What is Mu?

Scientifically known as B.1.621, the WHO designated Mu a variant of interest on August 30, because it might have immune escape properties. It also means WHO considers it worthy of special monitoring but it is still less of a potential threat than the Delta or Alpha strains. Delta and Alpha are more dangerous due to their increased virulence. Mu is not yet widespread across the globe. Its presence of 39 per cent in Colombia and 13 per cent in Ecuador makes it potentially risky.

What does the WHO say?

There have been a few sporadic reports of cases of the Mu variant. Some larger outbreaks have been reported from South America and Europe. Although the global prevalence of the Mu has declined and is currently below 0.1 per cent, the prevalence in Colombia and Ecuador has consistently increased, said the global health body in its weekly update.

What is a variant of interest?

A variant with genetic mutations that affect or can affect the virus's characteristics, such as transmissibility, the severity of the disease it can cause, immune escape, etc is called a variant of interest.

How is it different from the variant of concern?

After meeting the definition of a variant of interest, if it shows increased transmissibility or detrimental change in COVID-19 epidemiology, it is designated a variant of concern. Also, if it is associated with a decrease in the effectiveness of public health and social measures or available diagnostics, vaccines, therapeutics, it is a variant of concern, says the WHO.

How are variants named?

The scientific community uses an established system of nomenclature for naming and tracking new variants of a virus. WHO convened a group of scientists, other experts, and agencies to consider easy-to-pronounce and non-stigmatising labels. The experts recommended using letters of the Greek Alphabet – Alpha, Beta, Gamma, Delta – for now to designate the variants of SARS-CoV-2.

Mu is the 12th letter of the Greek alphabet.