Some 426 cases of the BA.2 variant have been confirmed in the UK to date, with the earliest dated December 6.
The largest number of confirmed cases was in London, with 146 positive BA.2 infections followed by the south-east region with 97.
More than 8,000 cases of BA.2 have been identified in 40 countries worldwide.
Denmark has seen 6,411 confirmed cases of “stealth Omicron”.
India has seen 530, Sweden 181 and Singapore 127 positive infections from BA.2.
At this point it is not possible to determine where the sublineage may have originated, the UK Health Security Agency (UKHSA) said.
Dr Meera Chand, Covid-19 Incident Director at UKHSA, said: “It is the nature of viruses to evolve and mutate, so it’s to be expected that we will continue to see new variants emerge as the pandemic goes on.
“So far, there is insufficient evidence to determine whether BA.2 causes more severe illness than Omicron BA.1, but data is limited and UKHSA continues to investigate.”
Public health bosses announced they were investigating the new variant of Covid-19, nicknamed “stealth Omicron” earlier this month.
Earlier this month on January 10, the UKHSA regarded BA.2 as a “variant under investigation” which is one below a “variant of concern”.
Scientists have been speaking out on the topic.
Virologist Tom Peacock of Imperial College London tweeted: “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.”Mr Peacock added: “There is likely to be minimal differences in vaccine effectiveness against BA.1 and BA.2. Personally, I’m not sure BA.2 is going to have a substantial impact on the current Omicron wave of the pandemic.
“Several countries are near, or even past the peak of BA.1 waves. I would be very surprised if BA.2 caused a second wave at this point. Even with slightly higher transmissibility this absolutely is not a Delta-Omicron change and instead is likely to be slower and more subtle.”
It comes as the World Health Organisation’s (WHO) Europe director said the Covid-19 pandemic is heading towards its “endgame” in Europe due to the milder Omicron variant.
Hans Kluge said it was “plausible” the region is moving towards a “kind of pandemic endgame” and the Omicron variant could infect up to 60 per cent of Europeans by March.
But Dr David Nabarro, the WHO’s special envoy for Covid-19, urged caution.
He said on Monday: “The end is in sight, but how long is it going to take to get there? What sort of difficulties will we face on the way? Those are the questions that none of us can answer because this virus continues to give us challenges and surprises.”
He added: “It’s as though we’re just passing the halfway mark in a marathon and we can see that yes, there is an end and fast runners are getting through ahead of us.
“But we’ve still got a long, long way to trudge and it’s going to be tough.”