Clash of the mutants

Double mutant variant. Triple mutant. Confused? THE WEEK decodes the mutations and variants of an evolving virus

- REKHA DIXIT

Mea culpa, rues Anurag Agarwal. Head of the CSIR-Institute for Genomics and Integrative Biology (CSIR-IGIB) in New Delhi, Agarwal coined the term ‘double mutant’, which has become the buzzword in India now. But he says he never intended it to be part of the common parlance.

“We were writing a scientific note, where we were describing a new Variant of Concern (VoC) that had been found,” says Agarwal. This variant of the SARS-CoV-2 virus, which they first identified in Maharashtra, had several mutations, as is the normal case with newer generations of viruses. However, among those mutations, two were of particular interest, since they showed “immune escape” in vitro. This means that when geneticists cultured virus genomes in the lab and subjected them to extreme antibody pressure, which should effectively neutralise the virus, some mutations still survived.

Using a method of nomenclature called Pango (there are multiple nomenclature methods, which cause much confusion even among the scientific community, forget laypersons), they identified this variant by a most uninteresting sounding name called B.1.617, flagging two of the various mutations. These mutations are E484Q and L452R, which are simply codes for the point on the genome at which a particular amino acid (indicated by the letter) is replaced by another. “While writing the paper, we had to repeatedly talk about the variant, and I referred to it at some point as the double mutant,” explains Agarwal.

This catchy word was first heard in public on March 24, when Union health secretary Rajesh Bhushan used it in his briefing. And before they knew it, the term was bandied around by just about everyone. It also caused a measure of concern, with people beginning to mistakenly believe that the double mutation made the virus a worse enemy than the ancestral Wuhan strand.