We’ve all become familiar with virus mutations throughout the pandemic, and we can probably all list COVID variants, such as Alpha, Delta, and Omicron. But now we hear more and more about subvariants, as Omicron mutates into Omicron BA.2, Omicron BA.4, Omicron XE and more.
We know that the virus is mutating as it spreads, but when is a new mutation a new variant and when is it a subvariant? And what happens when they combine?
Read more: What’s the new variant of Omicron XE and should I worry?
First of all, what are mutations?
When cells reproduce, they use a set of genetic instructions (made of DNA or RNA) to replicate. But since this is happening at such a fast pace, mistakes can sometimes occur.
These errors, or changes in the genetic code, are also called mutations.
In complex organisms like humans, we are good enough to find and correct these mistakes. But when these research and repair processes fail, we see that diseases like cancer arise.
When errors occur during the copying of genetic material into viruses, most leave the genetic material too broken to continue replicating and this virus does not survive.
Read more: Why are there so many new Omicron subvariants, like BA.4 and BA.5? Will I be reinfected? Does the virus mutate faster?
Sometimes, by chance, these errors can occur in a section of the code that allows the virus to survive and, in the process, changes occur in the virus.
When it is in a part of the virus that determines how it behaves, it can change the properties of the virus.
It can change the severity of the disease it causes, our ability to diagnose the virus with our current tests, or even the proper functioning of treatments.
Since it was first reported in the Chinese city of Wuhan in December 2019, more than 520 million COVID cases have been reported worldwide (and probably many more unregistered cases). This means a lot of virus replication and a lot of opportunities for such changes to occur.
With more than 520 million infections worldwide, the virus has had many opportunities to replicate. Shutterstock
One of the reasons we have heard so much about such changes is our access to genomic sequencing, to determine the genetic code of the virus. This has allowed us to find even small changes in the virus’s 30,000 letter code, essentially in real time.
When these changes are found, the new virus can be described in many ways, especially depending on how different the genetic code and the resulting properties of the virus from the parent virus from which it originated.
Some terms also mean essentially the same thing and can be used interchangeably, depending on the field in which someone works. While there are many commonly used consensus terms, there are no simple universal definitions.
What are the variants? Are they different from the varieties?
One variant is where the genetic code has changed due to a mutation, or a series of mutations. One variant, although genetically different, does not necessarily differ in its behavior from the parent virus.
The virus that causes COVID is a single species of coronavirus called SARS-CoV-2. For many other viruses (and other organisms), there are multiple “strains” where there have been very significant changes not only in the genetic code, but also in the biological properties and behavior of the virus. In the same way, all dogs are of the same species but there are different breeds, which look and act very differently.
Some researchers would say that so far no SARS-CoV-2 has been found to differ enough to meet this definition, so for now, there is only one strain.
Other researchers, however, have suggested that variants that have shown different behaviors meet the definition of being different strains.
Others reiterate that a new variant that becomes dominant in a population gains the right to be called a strain.
The same species can have different types that behave differently. Shutterstock
What about the “interest” and “concern” variants?
To describe the impact of genetic changes on virus behavior, different types of variants have been described.
In collaboration with networks of experts, at the end of 2020, in the face of the emergence of variants that posed an increased risk, the World Health Organization (WHO) characterized “variants of interest” and “variants of concern “.
According to these WHO definitions, a “variant of interest” is a variant with genetic changes that are known or expected to affect important features of the virus. These include transmissibility, the severity of the disease, protection against immune responses, reduced ability to meet diagnostic tests, or the reduced effect of treatment.
Read more: Why COVID-19 variants are so dangerous and how to prevent them from spreading
To become a variant of concern, a new variant must also have been identified to cause a major transmission and to be thought to pose an emerging risk to public health.
Basically, once the potential of the property that turned it into a variant of interest has been found, a variant of interest will be known as a “variant of interest”.
What are subvariants?
Omicron has been shown to be more infectious than its predecessors, so it has spread rapidly around the world. Given the resulting abundant reproduction opportunities, Omicron has had the opportunity to acquire its own specific mutations.
These have not been considered significant enough to meet the definitions for new variants. However, they have had some slightly different properties.
For this reason they have been called “subvariants”. We initially saw BA.2 emerge, which was found to be slightly more infectious than the original Omicron, BA.1.
Read more: BA.2 is like Omicron’s sister. That’s all we know so far
What are recombinants?
There are now a large number of Omicron subvariants, including BA.4, BA.5, and BA.2.12.1. BA.4 was detected in January and is essentially a mixture of BA.1 and BA.3 with some new mutations, making it slightly more infectious than the previous subvariants.
When viruses reproduce within host cells, they can randomly pick up pieces of multiple strains or variants when they reproduce, if the host cell contains both strains or variants.
Since a combination of both viruses is basically formed, this process is called recombination. When this happens, the resulting “recombinant” may have properties of one or both viruses.