Health officials have warned about two mutant strains of coronavirus that have emerged in the UK.
Cases of variants BQ.1 and XBB have been recorded across the country, with the latter said to spread quickly and appearing to evade vaccine protection.
More than 700 cases of the BQ.1 variant have been logged in the UK. A further 18 cases of the so-called "nightmare variant" XBB - which is a mutation of Omicron - have also been recorded.
They have so far not been listed as variants of concern by the UK Health Security Agency, The Mirror reports.
It comes as scientists believe the so-called "nightmare variant" XBB variant may be behind the recent spike in Covid cases in Singapore, although one expert said the variant is "no different from the others".
Dr Meera Chand, director of clinical and emerging infection at the UKHSA said: "It is not unexpected to see new variants of SARS-CoV-2 emerge.
"Neither BQ.1 nor XBB have been designated as Variants of Concern and UKHSA is monitoring the situation closely, as always.
"Vaccination remains our best defence against future COVID-19 waves, so it is still as important as ever that people come take up all the doses for which they are eligible as soon as possible."
Infectious disease expert John Swartzberg previously told the San Francisco Chronicle : "We are seeing a slew of new variants that are using a similar approach to survive — they are finding ways to evade the way we get immunity from vaccines and previous infection with changes on the spike protein.
"XBB is no different from the others."
XBB was first found in India in August and has since been found in Bangladesh, Japan, Singapore and at least 13 more countries - including Australia and Denmark.
It has also been found in Hong Kong. Singapore Ministry of Health said XBB went from being responsible for 22% of cases to being responsible for 54% of cases in one week. 79% of people in Singapore are fully vaccinated.
Singapore’s health ministry said there is no evidence that XBB causes more severe illness, although it appears resistant to treatments.
Singapore saw the number of new cases of Covid double from 4,719 on 10 October to 11,732 on October 11, according to Johns Hopkins’s Coronavirus Resource Center.
Singapore health minister Ong Ye Kung said the country is likely to see 15,000 daily cases on average by mid-November.
XBB is a mutation on Omicron BA.2. 23 cases of XBB have been detected in the USA.
Natalie Thornburg, CDC lead respiratory virus immunology specialist said: "XBB is a chimera. I think there have been a couple of sequences identified in the United States. But it’s way, way, way, way below that 1% threshold. I mean, it’s really like a handful of sequences."
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