The government has confirmed it is monitoring a sub-variant of Omicron that scientists fear could be more transmissible – but experts caution very little is currently known about it.
Most cases of Omicron are the BA.1 variant, but recently a new sister variant known as BA.2 has been detected in many countries across the world.
It was first designated as a variant on 6 December.
BA.2 shares similarities with BA.1, and they are both considered to be Omicron.
However, it has different S-gene mutations compared to BA.1, which means when carrying out a PCR test BA.2 shows positive for the S-gene while BA.1 does not.
The fact BA.1 lacked the S-gene was key to detecting and tracking the spread of Omicron early on.
BA.2 is spreading quickly in places like India and the Philippines, and early signs show it is growing in the UK, Germany and Denmark.
This indicates it may be more transmissible than BA.1, but so far there is no conclusive evidence, experts warn.
The UK Health Security Agency (UKHSA) noted a growth in the number of BA.2 cases was first detected on 3 January.