The deadly 'Kraken' coronavirus variant, as well as the CH.1.1 variant, are expected to take over and become the dominant strains in the UK, experts have warned.
The XBB.1.5 variant has been increasing in the USA in recent months, the UK Health Security Agency (UKHSA) said.
Currently, Covid cases in the UK are mainly made up of BQ.1 and its sublineages, the UKHSA added.
A risk assessment found that two variants, CH.1.1 and XBB.1.5 - both part of the Omicron family - are most likely to take over from BQ.1 as the next dominant variant in the UK.
Dr Meera Chand, Director of Clinical and Emerging Infections, UKHSA said: "Through our genomic surveillance we continue to see evolution of variants in the Omicron family.
"UKHSA is constantly monitoring the situation and working to understand the implications for public health.
"Vaccination remains our best defence against future COVID-19 waves, so it is still as important as ever that people come forward and take up all the doses for which they are eligible as soon as possible."
It comes after the number of Covid infections reached its highest level since last summer.
Figures from the Office of National Statistics showed the number of people likely to have coronavirus over Christmas was a huge 2.9million.
The concerning number is more than double the number at the start of December and the highest total since mid-July.
Michelle Bowen, ONS head of health surveillance, said infections have risen across the whole of the UK, with levels in Northern Ireland now at their highest since March 2022.
She added: "Across English regions, infections have increased in the North East, Yorkshire and the Humber, the East Midlands, the East of England, the South East and the South West.
"Cases have also increased in those aged two to school Year 6, and those aged 50 years and over."
About one in 20 people in England are likely to have had Covid-19 over the festive period, along with one in 18 in Wales and one in 16 in Northern Ireland.
