We are now seeing cases of a sub-version of Omicron, known as BA.2, emerge in Australia and more than 50 countries.
It is more helpful to think of BA.2 as a sister of Omicron, rather than a daughter of the Omicron type BA.1 (or B.1.1.529).
Remind me, what is a type?
Viruses, and especially RNA viruses such as SARS-CoV-2, make a lot of mistakes when reproducing. They cannot 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 is referred to as a variant.
Omicron is a “highly divergent” variant, which has accumulated over 30 mutations in the spike protein. This has reduced the protection of antibodies from both prior infection and vaccination, and increased transmission efficiency.
When do health officials worry about the new version?
If the change in the genetic code is thought to have the potential to affect the properties of the virus that make it more harmful, and significant transmission occurs in many countries, it would be considered a “type of interest”.
If a variant of interest has been shown to be more infectious, avoid protection from vaccination or previous infection, and/or affect the performance of tests or treatments, it is labeled a “type of concern”.
The World Health Organization (WHO) on 26 November classified Omicron as a Type of Concern because of its high re-infection rate, increased transmissibility and likely to be due to low vaccine safety.
What is Omicron Lineage?
A lineage, or sub-variant, is a genetically closely related group of virus variants derived from a common ancestor.
The Omicron version includes three sub-lineages: B.1.1.529 or Ba.1, Ba.2 and Ba.3.
While the WHO has not given BA.2 a separate classification, the United Kingdom has labeled BA.2 a type “under investigation”. So there isn’t a sort of interest or concern based on the WHO’s definitions so far, but one that’s being watched closely. ,
This is not the first version with sub-lineages. Late last year, Delta “Plus” or AY.4.2 was widely reported, then Omicron came along.
What’s different about BA.2?
While the first sequences of BA.2 were presented from the Philippines – and we have now seen thousands of cases, including some in the USA, UK and Australia – its origin is still unknown.
The exact properties of BA.2 are also being investigated. Although there is no evidence yet that it causes more serious disease, scientists have some particular concerns.
1. Hard to differentiate
One marker that helped differentiate Omicron (BA.1) from other SARS-CoV-2 variants on PCR tests is the absence of the S gene, known as “S gene target failure”. But this is not the case with BA.2. ,
The inability to trace this lineage in this way has led some to label it as a “stealth subspecies”.
But that doesn’t mean we can’t diagnose BA.2 with PCR tests. It simply means that when someone tests positive for SARS-CoV-2, it will take us a little longer to know through genome sequencing which variant is responsible. Same was the case with the previous variants.
2. It Can Be More Contagious
Perhaps most concerning is the emerging evidence that BA.2 may be more infectious than the original Omicron, BA.1.
A preliminary study from Denmark, where BA.2 has largely replaced BA.1, suggests that BA.2 increased susceptibility to infection only two-fold in unvaccinated people compared to BA.1 gives.
The researchers suggest that people who were fully vaccinated are 2.5 times more susceptible to BA.2 than those who were vaccinated, and those who were vaccinated with a booster vaccine are about three times more susceptible.
The study examined more than 2,000 primary household cases of BA.2 to determine how many cases occurred during a seven-day follow-up period.
The researchers estimated the secondary attack rate (basically, the probability infection occurs) for families infected with BA.1 to be 29%, compared to 39% for those infected with BA.2.
This Danish study is still an imprint, which means it has yet to be tested by independent scientists, so more research is needed to confirm whether BA.2 is indeed more contagious than BA.1.
We are likely to see new variants We should expect new variants, sub-variants and lineages to emerge. With such high levels of transmission, there is abundant opportunity for the virus to reproduce and errors or mutations to arise.
The way to address this, of course, is to try to slow transmission and reduce the susceptible pool of hosts in which the virus can replicate freely.
Strategies such as social distancing and wearing masks, as well as increasing vaccination rates globally, will slow the emergence of new variants and lineages. (Conversation)
by Paul Griffin, University of Queensland
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