Follow us for updates
© 2022 reportr.world
Read the Story →

What is Stealth Omicron? Here's What We Know So Far

Think of it as a sibling of the original strain.
Feb 3, 2022
Photo/s: Jerome Ascaño
Shares

By The Conversation via Reuters Connect

Cases of the SARS-CoV-2 variant omicron have escalated globally over the past two months, with many countries experiencing peaks higher than previous variants.

Now we’re seeing cases of a sub-variant, known as "stealth omicron" or BA.2, emerge in more than 50 countries, including the Philippines.

Rather than a daughter of the Omicron variant BA.1 (or B.1.1.529), it’s more helpful to think of BA.2 as Omicron’s sister.

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.

Continue reading below ↓

If changes in the genetic code are thought to have the potential to impact properties of the virus that make it more harmful, and there’s significant transmission in multiple countries, it will be deemed a “variant of interest”.

If a variant of interest is then shown to be more infectious, evade protection from vaccination or previous infection, and/or impact the performance of tests or treatments, it is labelled a “variant of concern”.

The World Health Organization (WHO) classified Omicron a variant of concern on November 26 because of its potential to cause higher reinfection rates, increased transmissibility and reduced vaccine protection.

ALSO READ:

'Stealth Omicron' More Infectious Than Original Strain: Study 

'Stealth Omicron' is Detected in the Philippines, Here's What We Know So Far

'Stealth Omicron' Found in 57 Countries, WHO Says

A lineage, or sub-variant, is a genetically closely related group of virus variants derived from a common ancestor.

Continue reading below ↓
Recommended Videos

The Omicron variant comprises 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 labelled BA.2 a variant “under investigation”. So not yet a variant of interest or concern, based on WHO definitions, but one that is being watched closely.

This is not the first variant to have sub-lineages. Late last year, Delta “plus” or AY.4.2 was reported widely, then Omicron came along.

While the first sequences of BA.2 were submitted from the Philippines – and we have now seen thousands of cases, including in the United States, the UK and some in Australia – its origin is still unknown.

The exact properties of BA.2 are also still being investigated. While there is no evidence so far that it causes more severe disease, scientists do have some specific concerns.

It’s harder to differentiate

A marker that helped differentiate Omicron (BA.1) from other SARS-CoV-2 variants on PCR tests is the absence of the the S gene, known as “S gene target failure”. But this is not the case for BA.2.

Continue reading below ↓

The inability to detect this lineage in this way has led some to label it the “stealth sub-variant”.

But it doesn’t mean we can’t diagnose BA.2 with PCR tests. It just means when someone tests positive for SARS-CoV-2, it will take us a little longer to know which variant is responsible, through genome sequencing. This was the case with previous variants.

It may be more infectious

Perhaps most concerning is emerging evidence 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 BA.2 increases unvaccinated people’s susceptibility of infection by just over two times when compared to BA.1.

The researchers suggest fully vaccinated people are 2.5 times more susceptible to BA.2 than BA.1, and those who were booster vaccinated are nearly three times more susceptible.

The study examined more than 2,000 primary household cases of BA.2 to determine the number of cases that arose during a seven-day follow up period.

Continue reading below ↓

The researchers also estimated the secondary attack rate (basically, the probability infection occurs) to be 29% for households infected with BA.1 versus 39% for those infected with BA.2.

This Danish study is still a preprint, meaning it’s yet to be checked by independent scientists, so more research is needed to confirm if BA.2 is truly more infectious than BA.1.

We should expect new variants, sub-variants and lineages to continue to emerge. With such high levels of transmission, the virus has abundant opportunity to reproduce and for errors or mutations to continue 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 freely replicate.

Strategies such as social distancing and mask-wearing, as well as increasing vaccination rates globally, will slow the emergence of new variants and lineages.

About the author:  is an Associate Professor of Infectious Diseases and Microbiology at The University of Queensland.

Continue reading below ↓

Reportr is now on Quento. Download the app or visit the Quento website for more articles and videos from Reportr and your favorite websites.

Latest Headlines
Read Next
Recent News
Some relief from rising prices.
With the reopening of several local destinations, this app has never been more timely.
Landmark Roe vs Wade ruling of 1973 is overturned.
Its rise mirrors the rise of technology for the masses.
It cites global uncertainties for its move.
The news. So what? Subscribe to the newsletter that explains what the news means for you.
The email address you entered is invalid.
Thank you for signing up to On Three, reportr's weekly newsletter delivered to your mailbox three times a week. Only the latest, most useful and most insightful reads.
By signing up to reportr.world newsletter, you agree to our Terms of Service and Privacy Policy.