More than 400 cases of a new Omicron sub-variant have been identified in England.

       The UK Health Security Agency has described Omicron BA.2 as a “variant under investigation”.

       So far, 426 infections have been confirmed in England.

       Early analysis suggests it may spread faster than Omicron, though scientists are not certain of this and it has not been designated a “variant of concern”.

       It is not known if BA.2 causes more severe disease than the original Omicron variant.

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       The areas with the most confirmed cases are London, with 146, and the South East, with 97. The earliest dates to 6 December.

       It is also not clear where the sub-variant first emerged, but the new strain has been reported in 40 countries, including Denmark, India, Sweden and Singapore, according to the UKHSA.

       In Denmark, BA.2 has risen rapidly. It accounted for 20% of all Covid cases in the last week of 2021, increasing to 45% in the second week of 2022.

       Initial analysis made by Denmark’s Statens Serum Institut (SSI) showed no difference in hospitalisations for Omicron BA.2 compared to BA.1.

       SSI researcher Anders Fomsgaard said he did not yet have a good explanation for BA.2’s rapid growth. He said he was puzzled rather than worried.

       “It may be that it is more resistant to the immunity in the population, which allows it to infect more. We do not know yet,” he told local media.

       He added there was a possibility people infected with BA.1 might not be immune from catching BA.2 soon after.

       “It is a possibility,” he said. “In that case, we must be prepared for it. And then, in fact, we might see two peaks of this epidemic.”

       Dr Meera Chand, incident director at the UKHSA, said it is natural for viruses to mutate.

       “It’s to be expected that we will continue to see new variants emerge,” she said. “Our continued genomic surveillance allows us to detect them and assess whether they are significant.”

       The UKHSA is investigating the strain. In a statement, it said: “As is routine for any new variants under investigation, UKHSA is carrying out laboratory and epidemiological investigations to better understand the characteristics of this variant.

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       “We will continue to monitor this situation closely and recommend appropriate public health measures if needed.

       “More detail will be available in UKHSA’s regular Variant Technical Briefings.”