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 the world is seeing cases of a sub-variant of Omicron, known as BA.2, emerge in Australia and more than 50 countries.
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.
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”.
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.
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.
The inability to detect this lineage in this way has led some to label it the “stealth sub-variant”.
But it doesn’t mean people can’t diagnose this sub-variant 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.
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 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.
More research is needed to confirm if BA.2 is truly more infectious than BA.1.
Scientists predict 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 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.
Original content from The Conversation Australia. Note: Content has been edited for style and length.
Nina Alvarez is a Content Producer for Healthcare Channel. Her interests include writing, particularly about the healthcare sector and the many ways it can improve to further benefit people from all walks of life.