Why are there so many new Omicron subvariants, such as BA.4 and BA.5? Does the virus mutate faster? | Sebastian Duchene and Ashleigh Porter for the conversation

Band now many of us will be familiar with the Omicron variant of Sars-CoV-2, the virus that causes Covid. This variant of concern has changed the course of the pandemic, causing a dramatic increase in cases worldwide.

We also hear more and more new variants of Omicron with names like BA.2, BA.4 and now BA.5. The concern is that these subvariants can cause people to become infected again, leading to a further increase in cases.

Why are we seeing more of these new subvariants? Does the virus mutate faster? And what are the implications for Covid’s future?

Why are there so many types of Omicron?

All viruses, including Sars-CoV-2, are constantly mutating. The vast majority of mutations have little or no effect on the ability of the virus to be transmitted from one person to another or to cause serious illness.

When a virus accumulates a substantial number of mutations, it is considered a different lineage (a bit like a different branch in a family tree). But a viral lineage is not labeled as a variant until it has accumulated several unique mutations known to improve the virus’s ability to transmit and / or cause more serious disease.

This was the case with the BA lineage (sometimes known as B.1.1.529) which the World Health Organization labeled Omicron. Omicron has spread rapidly, representing almost all current cases with genomes sequenced worldwide.

Because Omicron has spread rapidly and has had many opportunities to mutate, it has also acquired its own specific mutations. These have given rise to various underlines, or subvariants.

The first two were labeled BA.1 and BA.2. The current list now also includes BA.1.1, BA.3, BA.4 and BA.5.

We saw variants of earlier versions of the virus, such as Delta. However, Omicron has surpassed these, potentially due to their higher transmissibility. Thus, subvariants of previous viral variants are much less common today and there is less emphasis on tracking them.

Why are subvariants a big problem?

There is evidence that these Omicron subvariants, specifically BA.4 and BA.5, are especially effective in reinforcing people with previous BA.1 infections or other lineages. There is also concern that these subvariants could infect people who have been vaccinated.

So we expect to see a rapid increase in Covid cases in the coming weeks and months due to reinfections, which we are already seeing in South Africa.

However, recent research suggests that a third dose of the Covid vaccine is the most effective way to slow the spread of Omicron (including subvariants) and prevent Covid-associated hospital admissions.

Recently, BA.2.12.1, has also attracted attention because it has spread rapidly in the US and has recently been detected in wastewater in Australia. Alarmingly, even if someone has been infected with the Omicron BA.1 subvariant, reinfection is still possible with the BA.2, BA.4, and BA.5 sublinings because of their ability to escape. immune responses.

Does the virus mutate faster?

You might think that Sars-CoV-2 is a super fast leader in mutations. But the virus actually mutates relatively slowly. Influenza viruses, for example, mutate at least four times faster.

Sars-CoV-2, however, has “mutant sprints” for short periods of time, our research shows. During one of these sprints, the virus can mutate four times faster than normal for a few weeks.

After these sprints, the lineage has more mutations, some of which may provide an advantage over other lineages. Examples include mutations that can help make the virus more transmissible, cause more serious illnesses, or evade our immune response, and so we have new emerging variants.

It is unclear why the virus suffers from mutational sprints that lead to the appearance of variants. But there are two main theories about the origins of Omicron and how it accumulated so many mutations.

First, the virus may have evolved into chronic (prolonged) infections in immunosuppressed people (they have a weakened immune system).

Second, the virus could have “jumped” to another species, before re-infecting humans.

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 only one patient became infected with BA.1 and BA.2 at a time. This coinfection caused a “genome exchange” and a hybrid variant.

Other cases of recombination in Sars-CoV-2 between Delta and Omicron have been reported, leading to what has been called Deltacron.

To date, recombinants do not appear to have higher transmissibility or cause more severe results. But that could change quickly with new recombinants. So scientists are monitoring them closely.

What could we see in the future?

As the virus circulates, we will continue to see new lineages and virus variants. Since Omicron is the most common variant today, we are likely to see more Omicron subvariants, and even recombinant lineages.

Scientists will continue to track new mutations and recombination events (especially with subvariants). They will also use genomic technologies to predict how they may occur and any effects they may have on the behavior of the virus.

This knowledge will help us limit the spread and impact of variants and subvariants. It will also guide the development of effective vaccines against multiple or specific variants.

Sebastian Duchene is an ARC DECRA Fellow at the University of Melbourne and Ashleigh Porter is a Research Officer at the Peter Doherty Institute for Infection and Immunity. This article was republished from The Conversation. Read the original here.

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