Tuesday, June 01, 2021

What do all those B.1.1.7, B.167.2, etc, variants mean?

Have you ever wondered where those variant labels like B.1.1.7, B.1.617, B.1.135 and P.1 actually come from? They were introduced partly to avoid any stigma from labels like "British variant", "Indian variant", "South African variant", "Brazilian variant", etc, and partly also, I imagine, so as to sound a bit more "scientific". But what do the numbers and letters mean?

The labelling system is known as the "Pango nomenclature", and it was developed by British scientists as a simple and adaptable way of identifying mutations as the virus evolved. It has now become the default method of identifying virus variants worldwide.

When the COVID virus (SARS-CoV-2) emerged in China in late 2019 and early 2020, two main strands were identified, reasonably enough, as A and B. As these initial strands started to evolve into variants, new lineages were designated A.1, A.2, etc, and B.1, B 2, etc. For unknown epidemiological reasons, the B strains were the main ones that escaped into the wider world. 

When these lineages started to develop their own mutations, they were identified with A.1.1, B.1.1, etc, and mutations of these lineages A.1.1.1, B.1.1.1, etc. B.1.1.7 identifies the seventh-discovered descendent of the sub-lineage B.1.1, and this is the highly-contagious variant of concern often referred to as the "British variant" or "Kent variant". B.1.167.2 is therefore the second-identified mutation of the 167th sub-lineage of the B.1 strand of the virus (three separate variants of the "Indian" B.1.167 lineage have been identified so far).

And that P.1 variant, the variant formerly known as the "Brazil variant"? Well, at some point, it was decided that the numbers were becoming too unwieldy, so some aliases were set up. For example, B.1.1.1.1, a sub-lineage first discovered in South Africa, was given the alias C.1. Later, D.1, E.1, etc, followed, as well as sub-lineages like C.1.1, C.2., D.1.1, etc. P.1 is actually an alias for B.1.1.28.1. And, of course, there is a P.1.1, P.1.2, P.2, etc. If you ask me, this has made things more confusing than before, but then I don't have to work with them all day long.

So, there you go. They are not just random numbers after all. If you want a full list of Pango lineages, you can find it here., 

However, just when we have pretty much got used to those labels, the World Health Organization (WHO) has started to popularize a new variant naming system using Greek letters, at least for the most common variants of concern.

For example: B.1.1.7, first identified in The UK, will be Alpha; B.1.135, first identified in South Africa, is Beta; P.1, first seen in Brazil, is Gamma; and the main Indian variant, B.1.167, is Delta. The idea is to simplify it for the general public; scientists will continue to use the existing number system (there are way more than four variants currently - the list of Pango lineages lists hundreds).

The WHO says that, when the 24 letters of the Greek alphabet have been exhausted (a scary propspect!), they will start another similar series. The Mesopotamian alphabet, perhaps?

So now, do we have to say "B.1.167, the variant first identified in India, also known as Delta"? (I read that very phrase in an article just today). And this is progress?

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