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Cases of the "more transmissible" Omicron sub-lineage BA.2 are increasing in the UK.
The UK Health Security Agency (UKHSA) has designated BA.2 as a “variant under investigation”, with initial data suggesting it could be more transmissible than the original strain of Omicron.
The proportion of BA.2 cases increased from 0.2% of cases to 0.8% between 8 and 15 January, according to genomics researchers are the Wellcome Sanger Institute.
BA.2 now makes up a higher proportion of cases than the Delta variant, which was dominant before Omicron.
Watch: BA.2 the Omicron sub-variant: everything we know
Should we be worried about BA.2?
The number of confirmed cases of BA.2 in the UK is currently low, with 426 infections confirmed by the UKHSA.
However, this number is not representative of the true figure, due to limited testing and sequencing.
The UKHSA said early analysis suggested BA.2 has an increased growth rate compared to the original Omicron lineage, BA.1, and so may be more infectious.
Dr Meera Chand, incident director at the 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.
"Our continued genomic surveillance allows us to detect them and assess whether they are significant."
UKHSA added that 40 countries had reported BA.2 sequences, with the most samples reported in Denmark, followed by India, Britain, Sweden and Singapore.
In Denmark, BA.2 has grown rapidly. It accounted for 20% of all COVID cases in the last week of 2021, rising to 45% in the second week of 2022.
A World Health Organization (WHO) report said: “While the BA.1 lineage has previously been the most dominant, recent trends from India, South Africa, the United Kingdom, and Denmark suggest that BA.2 is increasing in proportion.
“Drivers of transmission and other properties of BA.2 are under investigation but remain unclear to date.”
Anders Fomsgaard, researcher at the Danish Statens Serum Institut (SSI), said he did not yet have a good explanation for the rapid growth of the sub-lineage, adding he was puzzled, but not 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 broadcaster TV 2, adding that there was a possibility that people infected with BA.1 might not be immune from then 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."
The initial analysis made by Denmark's SSI showed no difference in hospitalisations for BA.2 compared to BA.1.
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