A coronavirus strain branded ‘stealth Omicron’ now accounts for 1.4% of Covid infections in Bristol, according to a sample of more than 200 positive cases.
Cases of the Omicron sub-variant BA.2 have been in the UK for some time - the first example was found on December 6, 2021.
But numbers are growing both here and abroad, and the UK Health Security Agency named it a ‘variant under investigation’ on January 21.
Early analysis suggests it has a faster growth rate than the Omicron strain currently dominant in the UK, BA.1, but there is not enough evidence to say whether it causes more severe illness.
The Wellcome Sanger Institute analysed 38,000 positive Covid-19 tests taken in the week to January 15 to determine which variant they were.
It found one in 100 samples were now Stealth Omicron across England.
It analysed 212 tests from Bristol, successfully identifying a variant in 211 of them.
BA.2 was found in three tests, representing 1.4% of those identified.
Elsewhere, in South Gloucestershire, 0.7% of 145 positive tests were found have BA.2, in North Somerset, 0.9% of 114 tests, and in Bath and North East Somerset, none of 95 tests.
It is not known where Stealth Omicron originated, with the first cases found in the Philippines and high numbers being reported in Denmark.
It got its nickname because it does not exhibit a tell-tale marker on its spike protein, revealed through a common type of PCR test, which the authorities had previously used to monitor the spread of Omicron.
But both PCR and lateral flow tests still identify Covid infection.
Dr Meera Chand, COVID-19 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 as the pandemic goes on.
“Our continued genomic surveillance allows us to detect them and assess whether they are significant.
“So far, there is insufficient evidence to determine whether BA.2 causes more severe illness than Omicron BA.1, but data is limited and UKHSA continues to investigate.”
Health secretary Sajid Javid said: “Our exceptional vaccine rollout means the number of people severely affected by COVID-19 is low, and the UK’s innovation and research has discovered life-saving treatments for those most at risk from COVID-19.”
On Monday, Bristol City Council reported that the Covid infection rate in Bristol was 922 cases per 100,000 people - below the England average of 97.
The authority added that 191 people were in hospital with Covid in the city and the NHS remained under ‘extreme pressure’.
Of the almost 20,000 people who took a PCR test last week, 20% had a positive result for Covid.
From today (January 27), people are no longer required to wear a face covering in any setting - but the city council says this is still ‘strong advised’.