Why are there so many new Omicron sub-variants？
Why are there so many new Omicron sub-variants？
All viruses, SARS-CoV-2 included, mutate constantly. The vast majority of mutations have little to no effect on the ability of the virus to transmit from one person to another or to cause severe disease.
When a virus accumulates a substantial number of mutations, it’s considered a different lineage (somewhat like a different branch on a family tree). But a viral lineage is not labelled a variant until it has accumulated several unique mutations known to enhance the ability of the virus to transmit and/or cause more severe disease.
This was the case for the BA lineage (sometimes known as B.1.1.529) the World Health Organization labelled Omicron. Omicron has spread rapidly, representing almost all current cases with genomes sequenced globally.
Because Omicron has spread swiftly, and has had many opportunities to mutate, it has also acquired specific mutations of its own. These have given rise to several sub-lineages, or sub-variants.
What we know about the latest Omicron sub-variants, according to the World Health Organization.
Why are the sub-variants a big deal?
There is evidence these Omicron sub-variants – specifically BA.4 and BA.5 – are particularly effective at reinfecting people with previous infections from BA.1 or other lineages. There is also concern these sub-variants may infect people who have been vaccinated.
So we expect to see a rapid rise in COVID cases in the coming weeks and months due to reinfections, which we are already seeing in South Africa.
However, recent research suggests a third dose of the COVID vaccine is the most effective way to slow the spread of Omicron (including sub-variants) and prevent COVID-associated hospital admissions.
What other tricks does the virus have?
Mutation is not the only way variants can emerge. The Omicron XE variant appears to have resulted from a recombination event. This is where a single patient was infected with BA.1 and BA.2 at the same time. This coinfection led to a “genome swap” and a hybrid variant.
Recombination through conifection
Two viruses can ‘swap’ genetic material, resulting in a recombinant virus that can become a distinct lineage (recombinant lineage X). Ashleigh Porter
Other instances of recombination in SARS-CoV-2 have been reported between Delta and Omicron, resulting in what’s been dubbed Deltacron.
So far, recombinants do not appear to have higher transmissibility or cause more severe outcomes. But this could change rapidly with new recombinants. So scientists are closely monitoring them.
What might we see in the future?
As long as the virus is circulating, we will continue to see new virus lineages and variants. As Omicron is the most common variant currently, it is likely we will see more Omicron sub-variants, and potentially, even recombinant lineages.
Scientists will continue to track new mutations and recombination events (particularly with sub-variants). They will also use genomic technologies to predict how these might occur and any effect they may have on the behaviour of the virus.
This knowledge will help us limit the spread and impact of variants and sub-variants. It will also guide the development of vaccines effective against multiple or specific variants.
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