The World Health Organisation says the subvariant of Covid dubbed Stealth Omicron is probably now outpacing the original as 8,000 cases have been found around the world.
The UK Health Security Agency has designated it a variant under investigation with fears it could be more transmissable and could better evade vaccines.
426 cases of the mutation have been found in the UK, and it has now been detected in 40 countries.
The variant, officially named BA.2, has been nicknamed Stealth Omicron as it cannot be distinguished from other variants of coronavirus using a PCR test - unlike Omicron.
Experts say the indications at the minute are that the speed of transmission and any ability to evade the vaccine are only slightly higher in BA.2.
Dr Tom Peacock told the Daily Mail : “Even with slightly higher transmissibility this absolutely is not a Delta to Omicron change, and instead is likely to be slower and more subtle."
He added: “Very early observations from India and Denmark suggest there is no dramatic difference in severity.”
