What is XBB.1.5? The 'wake-up call' COVID variant that's spreading in the UK

A new "highly transmissible" COVID-19 variant has emerged and is expected to push up case numbers in the coming weeks.

Experts have warned the rapid spread of XBB.1.5 in the US, which has driven up hospital admissions, should be a "wake-up" call for Britain as it already faces unprecedented pressures on its health service this winter.

Data suggests the variant already accounts for one in 25 cases in the UK, with studies showing it has developed a level of resistance to immunity.

Here's what you need to know about the XXB.1.5 variant

What is XBB.1.5? The variant is the latest offshoot of Omicron – the highly infectious version of COVID that sent cases in the UK soaring last winter. Various sub-variants of Omicron have evolved over the past year. XBB.1.5 evolved from XBB, which carried a mutation which helped the virus get past the body’s immune defences.

It XBB.1.5 more infectious? Evidence so far suggests XBB.1.5 has the ability to spread far faster than its predecessor. A senior World Health Organization (WHO) official described it as "the most transmissible sub-variant that has been detected yet".

Where is it spreading? In a matter of weeks, XBB.1.5 has become the dominant variant in the US, and is thought to make up 40% of COVID cases in the country – rising to 70% in hotspots. Early data suggests the new variant is behind one in 25 cases in the UK. The WHO said that XBB.1.5 “is on the increase in the US and Europe and has now been identified in more than 25 countries”.

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Where was XBB.1.5 first detected? The WHO says that XBB.1.5 was first discovered in October 2022. It was first detected in the New York City and Connecticut area, according to the Global Initiative on Sharing Avian Influenza Data.

How did it evolve? XBB.1.5 is a recombinant of two other Omicron sub-variants – in other words a hybrid. At some point, two different variants of COVID met – potentially in someone who caught multiple viruses at the same time – and swapped genetic information. They then will have re-combined, creating a version of the virus that has picked up advantages from both.

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Does XBB.1.5 cause more severe disease? So far, there is no evidence to suggest it is more dangerous than any other variants. However, the sheer number of cases are thought to be driving up hospitalisations in parts of the US, especially New York. The WHO said it is “following closely & assessing the risk of this subvariant & will report accordingly.”

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Will it cause a new wave in the UK? The jury is still out as to whether it will trigger a new wave in the UK. Director of the UCL Genetics Institute, Professor Francois Balloux, said that cases are “widely anticipated to go up in frequency globally”. Professor Paul Hunter, from the University of East Anglia told the BBC: "The balance of probabilities is that XBB.1.5 will trigger a wave here later this month, but we can't be sure."

How worried should we be? Experts have attempted to ease concerns. Professor Jonathan Ball, a molecular virologist at the University of Nottingham, said: “We’d better get used to the emergence of new variants, at least for the foreseeable future. Yes, they will lead to new waves of infection, but vaccination is still proving to be a very effective weapon to protect the most vulnerable from serious disease.”

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What is the advice from experts? The UKHSA is yet to classify XBB.1.5 as a variant of concern. However officials are urging the public to take sensible precautions to protect against COVID and other winter illnesses. In a statement relating to general pressures on the NHS, Professor Susan Hopkins said: “Adults should also try to stay home when unwell and if you do have to go out, wear a face covering. When unwell don’t visit healthcare settings or visit vulnerable people unless urgent.”