London, Jan 30 (IANS): The sub-variant of Omicron -- BA.2 -- feared to be even more infectious than its ancestor strain is behind one in 30 Covid-19 cases in England, according to official estimates, media reports say.

A report by the UK Health Security Agency found the mutant BA.2 sub-strain accounted for 3.4 per cent of the country's new infections by January 16 -- and it is doubling every week, the Daily Mail reported.

The growth advantage of the new variant is "substantial", the health agency claimed.

Scientists believe it may have evolved to be slightly more transmissible than the ancestral strain of Omicron and could slowly become the UK's dominant Covid variant.

It is already outcompeting its parent variant in Denmark but the country's government deemed the strain such a non-threat it this week announced it was ending all Covid restrictions, the report said.

Professor Paul Hunter, an epidemiologist at the University of East Anglia, told MailOnline there was no reason to panic about BA.2. He said it was not causing a "substantial difference to our current threat estimates".

There had been fears it might have been slipping past vaccine immunity more easily than Omicron, which would explain its evolutionary edge.

But UKHSA analysis found two and three vaccine doses work just as well against both strains -- providing about 70 per cent protection against symptomatic disease and even better immunity against severe outcomes.

Scientists have not yet been able to tell whether the sub-strain differs in severity from Omicron, which itself was a much milder variant than past strains. However, there is nothing to indicate the strain would be any more lethal.