The highly contagious coronavirus strain BA.2 is now responsible for more than four in five infections across England, research shows.
Researchers analysing positive COVID tests from the week to 12 March found 84% were the subvariant, branded ‘Stealth Omicron’.
That is up from 74% the week before.
The analysis by the Wellcome Sanger Institute comes as coronavirus infections and hospitalisations surge across the UK, with researchers saying the contagious subvariant is a key reason for the spike.
Stealth Omicron got its nickname because it is more difficult to differentiate from Delta than the original Omicron variant, BA.1.
It is also more contagious but early studies seem to show no greater risk of hospitalisation for an infected person, according to the UK Health Security Agency (UKHSA).
A spokesperson for the UKHSA said: “Omicron BA.2 is now the dominant variant in the UK, and has a significant growth advantage over Omicron BA.1.
“UKHSA continues to monitor all available data related to COVID-19 variants as a matter of routine, both in the UK and internationally.
“Vaccination provides a high level of protection against severe illness and it’s important that everyone has had their latest dose.
“We can all help reduce transmission by wearing a face covering in crowded or enclosed spaces, washing hands regularly and keeping rooms well ventilated.”
The Wellcome Sanger Institute analysed more than 41,000 COVID tests from the week ending March 12, taken from every part of England.
Regionally, London had the greatest proportion of samples testing positive for Stealth Omicron.
The region had 87.9% of samples testing positive, followed by the East of England with 85.6% and the North West with 85.1%.
The North East had the lowest positivity rate in England with 71.7% of samples testing positive for Stealth Omicron.
In the Liverpool City Region only one borough had a rate under the North West or England average.
Stealth Omicron in Liverpool City Region
Over 1100 test samples from across the six boroughs of the Liverpool City Region were tested by the Wellcome Sanger Institute and BA.2 was clearly the dominant variant.
Knowsley had the highest ratio in the region, with 91.1% of cases tested positive for BA.2 stealth Omicron - the 27th highest rate in England. One hundred and twelve COVID tests were analysed, with 102 identifying the variant.
In Liverpool, 89.6% of cases tested positive for BA.2 stealth Omicron - the 49th highest rate in England. Two hundred and forty-one COVID tests were analysed, with 216 identifying the variant.
Sefton had the third highest rate in the region as 87.6% of cases tested positive for BA.2 - with 233 from 266 tests identifying the variant.
In St Helens, 86.7% of cases tested positive for BA.2. Ninety COVID tests were analysed, with 78 identifying the variant.
In Wirral, 86.1% of cases tested positive for the stealth Omicron variant. Two hundred and eighty COVID tests were analysed, with 241 identifying the variant.
Halton had the lowest ratio in the region, with 82.9% of cases testing positive for the BA.2 stealth strain, with 97 from 117 tests identifying the variant.