A sub-lineage of the Omicron variant of coronavirus is able to spread faster than the original, analysis by the UK Health Security Agency (UKHSA) has found.
The UKHSA said BA.2 – a strain first detected in December – had a comparatively higher growth rate in all observed areas of England, meaning cases were increasing faster than they were for BA.1, known commonly as the Omicron variant.
Despite evidence of increased transmissibility, the new sub-variant was nowhere near becoming dominant in the UK.
It has not been classed as a “variant of concern” – as both Omicron and Delta were – but authorities are monitoring it closely.
Omicron remained the variant with the highest number of new cases, with 231,025 in the week to Wednesday 26 January according to government data.
There were 1,993 cases of BA.2 in the same period, the first in which it was monitored. By last Friday, 21 January, the government had detected 426 cases.
Dr Susan Hopkins, chief medical adviser for the UKHSA, said: “We now know that BA.2 has an increased growth rate, which can be seen in all regions in England.
“We have also learnt that BA.2 has a slightly higher secondary attack rate than BA.1 in households.
“Although hospitalisations and deaths remain low, cases are still high in some areas and some age groups so it’s important that we continue to act cautiously as restrictions are lifted.”
The UKHSA said there was yet to be any data on the severity of illness caused by BA.2 but tests were underway.
Early data suggests that vaccines were similarly effective against BA.2 and Omicron.
Jonathan Ball, professor of molecular virology, University of Nottingham, said: “It’s still early days, but the evidence so far suggests that BA.2 may be more transmissible than its close relative Omicron.
“However, the key issues are whether this variant is associated with more severe disease and if it can escape immunity delivered by vaccines.
“Early indicators suggest that the vaccines will provide similar levels of protection as we have seen for Omicron, so this is good news.
“Whether or not it causes more severe disease will become apparent as more data is collected.”
The World Health Organization has asked authorities to keep close track of BA.2 as it spreads around the world.
It said: “Investigations into the characteristics of BA.2, including immune escape properties and virulence, should be prioritised independently and comparatively to BA.1.”
The variant was thought to be in at least 40 countries at the start of this week, including the UK, Denmark, Singapore, India and Sweden.
Cases have grown fast in Denmark. Scientists think that more than 45 per cent of all new cases there are related to BA.2.
It is not yet clear where BA.2 emerged from, though the first cases were recorded in the Philippines.
