The WHO has added a fifth variant of interest (VOI), B.1.621.1, and labelled it the “Mu” variant on August 30, 2021. The other four current VOIs are Eta (B.1.525), Iota (B.1.526), Kappa (B.1.617.1) and Lambda (C.37).

The Mu variant was first identified in Colombia in South America in January 2021, where Mu has been detected in 39% of the samples analysed. From there, it has spread to other South American countries such as Ecuador (13%) and Chile (around 40%). The Mu variant has now been detected in 43 countries including the United States, United Kingdom, South Korea, Japan, Ecuador, Canada and parts of Europe. So far, it has not been detected in India.

There are more than 4700 cases of the Mu variant worldwide. Although with 2000 cases, the US has recorded the highest number of Mu cases, it is not yet regarded as an immediate threat.

In its Weekly epidemiological update on COVID-19 dated 31 August 2021, the WHO has said that “the Mu variant has a constellation of mutations that indicate potential properties of immune escape”. Preliminary evidence shows that these mutations may allow it to escape vaccine- and convalescent serum-induced antibodies, similar to the Beta variant.

The Mu variant has severe mutations such as T95I, Y144S, Y145N, R346K, E484K, N501Y, D614G, P681H, Y144T, K417N and D950N in the spike protein. Some of these mutations have been detected in the variants of concern. The N501Y and  P681H mutations are also present in the Alpha variant (B.1.1.7, first detected in the UK) and have been linked to rapid transmission. The N501Y mutation is also present in the Beta and Gamma variants of concern (VOC). The E484K and K417N mutations, which also occur in the Beta variant (B.1.351, first detected in South Africa) are associated with immune escape. However, the significance of other mutations is not yet known.

The Delta variant (B.1.617.2) continues to be the predominant variant across the world and the major cause of resurgence of cases in many parts of the world. At present, the Mu variant accounts for only 0.1% of cases globally, even though it has been around since January this year.

Although it is not a variant of concern (VOC) yet, it is being closely monitored to detect any changes that would make it more transmissible than the delta variant, cause more severe disease and make vaccines less effective. If this happens, it may be re-categorised as a VOC.

The best strategy to prevent emergence of new variants is to swiftly vaccinate as many people as possible. The larger the vaccinated population, the less the vulnerable population for the virus to infect and mutate. India administered more than 1.13 crore vaccine doses in the last 24 hours. This is the way to go.