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.
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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.
Should we be worried about BA.2?
There is no evidence on if BA.2 is more or less severe than other variants of COVID-19.
Tom Peacock, a virologist at Imperial College London, said the earliest indications from Denmark and India "suggest there is no dramatic difference in severity compared to BA.1".
Peacock also said: "There is likely to be minimal differences in vaccine effectiveness against BA.1 and BA.2."
He pointed to the fact several nations, including the UK, appear to be past their Omicron peaks and said he thinks it would be surprising if BA.2 caused another surge.
However, as almost all knowledge of Omicron on based on the BA.1 variant, there are uncertainties regarding BA.2.
The UKHSA said the government "continues to monitor variants including the BA.2 variant of Omicron (which is S-gene target positive). There is currently no evidence of BA.2 having a faster growth rate than the now widespread BA.1 variant."
The UKHSA noted 5% of COVID tests that have the S-gene are now BA.2 making S-gene tracking "no longer sufficient to assess the spread of Omicron as a whole".
COVID cases have been dropping sharply in recent weeks in the UK, but are still at highs previously considered unreachable.
Cases have dropped from highs of over 200,000 on 4 January to just over 100,000 on 20 January.
Prior to 21 December, the UK had never reported more than 100,000 cases in a single day.
Despite this hospitalisations only remain around half of what they were during the last peak in January 2021.
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