A question came up in comments and as is frequently the case, it led me on a treasure hunt. The omicron variant of SARS-CoV-2 is now being said to have multiple “sub-variants”. An article at The Conversation by Lara Herrero and Eugene Madzokere says this:
Errors often occur during the process of duplicating the viral RNA. This results in viruses that are similar but not exact copies of the original virus. These errors in the viral RNA are called mutations, and viruses with these mutations are called variants. Variants could differ by a single or many mutations.
Not all mutations have the same effect. To understand this better, we need to understand the basics of our genetic code (DNA for humans; RNA for SARS-CoV-2). This code is like a blueprint on which all organisms are built. When a mutation occurs at a single point, it won’t necessarily change any of the building blocks (called amino acids). In this case, it won’t change how the organism (human or virus) is built.
On occasion though, these single mutations occur in a part of the virus RNA that causes a change in a particular building block. In some cases, there could be many mutations that together alter the building block.
A variant is referred to as a strain when it shows distinct physical properties. Put simply, a strain is a variant that is built differently, and so behaves differently, to its parent virus. These behavioural differences can be subtle or obvious.
For example, these differences could involve a variant binding to a different cell receptor, or binding more strongly to a receptor, or replicating more quickly, or transmitting more efficiently, and so on.
Essentially, all strains are variants, but not all variants are strains.
while this article at The Conversation by Paul Griffin says this:
Viruses, and particularly RNA viruses such as SARS-CoV-2, make lots of mistakes when they reproduce. They can’t correct these mistakes, so they have a relatively high rate of errors, or mutations, and are constantly evolving.
When the genetic code of a virus changes as a result of these mutations, it’s referred to as a variant.
Omicron is a “highly divergent†variant, having accumulated more than 30 mutations in the spike protein. This has reduced the protection of antibodies from both prior infection and vaccination, and increased transmissibility.
and
A lineage, or sub-variant, is a genetically closely related group of virus variants derived from a common ancestor.
The Omicron variant comprises three sub-lineages: B.1.1.529 or BA.1, BA.2 and BA.3.
From which I infer several things:
- B.2 is genetically closely related to B.1, the originally detected form of the omicron variant. It’s therefore part of the omicron lineage, i.e. a sub-variant.
- It is not yet known whether B.2 has a behavioral difference from B.1. It might end up being designated a strain. We just don’t know yet.
- A lot of this stuff consists of judgment calls. To some extent they’re making it up as they go along.
Geert Vandan Bossche has speculated a variant might mutate where it will bind to another receptor, not the ACE one, where the current remedies and vaccines are targeting. This would render what we are using now, perhaps even the anti-virals, no longer viable for treatment.