A mutation of COVID-19 has been designated a “variant under investigation” by the UK Health Security Agency (UKHSA), after it emerged it may be more transmissible then Delta.

The variant – known as Delta AY.4.2 – was designated after the UKHSA said it has “become increasingly common in the UK in recent months”.

Delta AY.4.2 – which mutated from the Delta coronavirus variant – will now be monitored by scientists.

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The variant has been given the official name VUI-21OCT-01 and is not currently designated as a variant of concern.

As of 20 October, there were 15,120 cases of it in England – about 6% of all Delta cases, which itself makes up 99.8% of COVID-19 cases.

The UKHSA said: “The designation was made on the basis that this sub-lineage has become increasingly common in the UK in recent months, and there is some early evidence that it may have an increased growth rate in the UK compared to Delta.

“More evidence is needed to know whether this is due to changes in the virus’ behaviour or to epidemiological conditions.”

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The new variant has two mutations on its spike protein, according to the director of the UCL Genetics Institute, Professor Francois Balloux.

He said: “Most SARS-CoV-2 (the coronavirus which causes COVID) mutations have independently emerged many times in unrelated strains.

“Both the spike Y145H and A222V mutations have been found in various other SARS-CoV-2 lineages since the beginning of the pandemic, but have remained at low frequency until now.

“The first strains carrying both mutations were sequenced in April 2020. Neither are found in any variant of concern.”

The professor added that VUI-21OCT-01 remains rare outside of the UK, with three cases identified in the US.

“In Denmark, the other country that besides the UK has excellent genomic surveillance in place, it reached a 2% frequency but has gone down since. In addition, functional work is under way to test whether it may be less well recognised by antibodies,” he said.

“As VUI-21OCT-01 is still at fairly low frequency, a 10% increase in its transmissibility could have caused only a small number of additional cases. As such it hasn’t been driving the recent increase in case numbers in the UK.”

In the latest daily figures, another 49,298 new cases of COVID and 180 virus-related deaths were reported.

Variant offshoots are common and form when the virus makes mistakes as it copies itself to replicate.

Delta already has 45 such offshoots. The most common of which, AY.4, now accounts for 70% of all SARS-CoV-2 genomes sequenced worldwide.

AY.4 has given rise to two recognised offshoots, AY.4.1 and AY.4.2.

Dr Jenny Harries, chief executive of the UKHSA, said: “Viruses mutate often and at random, and it is not unexpected that new variants will continue to arise as the pandemic goes on, particularly while the case rate remains high.

“It is testament to the diligence and scientific expertise of my colleagues at the UKHSA, and the genomic sequencing capacity developed through the pandemic, that this new variant has been identified and analysed so quickly.

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“However, it should serve as objective evidence that this pandemic is not over.”

Her advice includes encouraging people to get vaccinated, wear facemasks in crowded settings and to keep windows open when meeting inside.

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