• Recently, the World Health Organisation (WHO) has added a new variant of Covid-19 in the list of Variants of Interest (VOI) and named it Mu (B.1.621). It has also added C.1.2 as a new VOI.
  • According to INSACOG (Indian SARS-CoV-2 Genomics Consortium), India has so far not seen Mu and C.1.2, and the Delta variant and its sub-lineages continue to be the main Variants of Concern (VOC).
  • 1.2 is a sub-lineage of the C.1 variant described in South Africa but did not spread globally.

Important points:

  • Mu belongs to the lineage B.1.621 variant and named after the twelfth letter of the Greek alphabet. It was first detected in Colombia in January 2021.
  • It has a constellation of mutations that indicate potential properties of immune escape. It has several substitutions affecting the Spike Protein and amino acid changes.
  • It has seen mutations, E484K, N501Y, P681H, D614G, which have been reported in other VOIs and VOCs.

It is the fifth ‘VOI’ to be monitored by WHO. The other four VOIs are:

  • Eta (lineage B.1.525), Iota (lineage B.1.526), Kappa (lineage B.1.617.1), and Lambda (lineage C.37).
  • A variant is placed 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”.
  • 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:
  • Alpha (lineage B.1.1.7, the so-called ‘UK variant’), Beta (lineage B.1.351, ‘South Africa variant’), Gamma (lineage P.1, ‘Brazil variant’), Delta (lineage B.1.617.2).

Mutation, Variant and Strain

  • When a virus replicates it doesn’t always manage to produce an exact copy of itself.
  • This means that, over time, the virus may start to differ slightly in terms of its genetic sequence.
  • Any changes to the viral genetic sequence during this process is known as a Mutation.
  • Viruses with new mutations are sometimes called Variants. Variants can differ by one or multiple mutations.
  • When a new variant has different functional properties to the original virus and becomes established in a population, it is sometimes referred to as a New Strain of the virus.
  • All strains are variants, but not all variants are strains.


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