An offshoot of the Omicron COVID-19 variant, which could be more infectious and harder to track, is spreading fast overseas.
The new strain known as BA.2 is a sister lineage to the current Omicron strain (BA.1). Both lineages are currently defined as the Omicron variant.
It's still unclear how much danger the new strain poses but scientists are hard at work trying to find out.
The UK Health Security Agency recently labelled BA.2 as a variant under investigation, one level below a variant of concern.
Where did BA.2 come from?
BA.2 is believed to have been first identified in late December 2021. Since then it has spread to around 40 countries and accounts for the majority of recent cases in places like India, Denmark and Sweden.
What do we know about it so far?
In early January, The World Health Organization (WHO) said BA.2's prevalence is increasing and could take over as the main Omicron strain in several countries.
"While the BA.1 lineage has previously been the most dominant, recent trends from India, South Africa, the United Kingdom, and Denmark suggest that BA.2 is increasing in proportion.
"Drivers of transmission and other properties of BA.2 are under investigation but remain unclear to date," The WHO said in an update on January 7.
The organisation also noted BA.2's ability to evade standard PCR testing making it more difficult to detect.
The WHO is yet to classify BA.2 as a variant of concern or a variant under monitoring. It says more research is needed to properly understand the strain.
How dangerous is BA.2?
There have been early indications the variant is more transmissible than Omicron but it's not yet known whether it's more dangerous.
In Denmark, where it accounts for nearly half of all Omicron cases, there hasn't been a stark change in hospitalisations which could be good news.
But Tom Peacock, a virologist at Imperial College London, said it's too early to conclusively tell how dangerous it is.
"Consistent growth across multiple countries is evidence BA.2 may be some degree more transmissible than BA.1," he said.
"Unfortunately this is really where the evidence mostly ends - we do not currently have a strong handle on antigenicity, severity or much evidence for how much more transmissibility BA.2 might have over BA.1 - however we can make some guesses/early observations.
"*Very* early observations from India and Denmark suggest there is no dramatic difference in severity compared to BA.1. This data should become more solid (one way or another) in the coming weeks."
The BA.1 Omicron variant is more transmissible than the Delta COVID-19 variant but so far is less severe.
However, the WHO has cautioned against describing it as "mild" pointing out the variant is still killing and hospitalising people across the world.
