How serious a threat is new Omicron Covid variant XBB.1.5?

An Omicron subvariant blamed for a surge in Covid cases in the US has been detected in the UK.

The rapid spread and “growth advantage” of Omicron XBB.1.5 – nicknamed the Kraken variant – is a “concern”, Maria Van Kerkhove, Covid-19 technical lead at the World Health Organization (WHO), told a press conference this week.

First identified in the US in October, the new subvariant is now “ripping through” Britain, said the Daily Express.

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How transmissible is XBB.1.5?

The new subvariant is another offshoot of Omicron, the highly transmissible strain that followed the Alpha, Beta, Gamma and Delta variants. Like other subvariants, XBB.1.5 was formed when fragments from other variants merged, probably when somebody was infected with two strains at the same time.

The WHO has warned that XBB.1.5 is “the most transmissible subvariant which has been detected yet”.

The new strain currently accounts for almost 41% of confirmed Covid-19 cases across the US, according to latest data from the Centers for Disease Control and Prevention.

The so-called Kraken strain is “spreading like wildfire”, said Fox News. Dr Marc Siegel, a clinical professor of medicine at NYU Langone Medical Center, told the broadcaster that each Omicron variant was “outcompeting its predecessor”.

In addition to being “highly immune evasive”, said CNN, XBB.1.5 has “an additional trick up its sleeve that seems to be helping to fuel its growth”. The subvariant has a “key mutation” that allows it to “bind more tightly” to ACE2, a protein on the surface of many cell types that acts as the “doors the virus uses to enter our cells”, the site explained.

Latest data suggests that XBB.1.5 is already behind one in 25 cases in the UK. However, the figures, from the Sanger Institute in Cambridge, were based on just nine samples in the week to 17 December, “so the UK will have to wait for more data in the coming weeks to get a better picture”, said ITV News.

Does it lead to move severe illness?

There is no evidence as yet that XBB.1.5 leads to more severe illness.

Previous subvariants of Omicron caused relatively mild illness, and “there’s no good reason why we might expect this one to be different”, Cambridge University's Professor Ravindra Gupta told ITV News.

Martin Michaelis, a professor of molecular medicine at the University of Kent, told Channel 4’s Fact Check that the various XBB subvariants of Covid “have not been clinically reported to cause more severe disease than previous Omicron subvariants”.

However, he cautioned that XBB strains, including XBB.1.5, are not well recognised by antibodies from Covid vaccines and previous infections, so “it is not yet clear what this means for the severity of the disease” that these subvariants cause.

The WHO is working on a new risk assessment of XBB.1.5 that is expected to be released soon.

Why is it called Kraken?

The Kraken is a “legendary octopus-like sea monster”, said ITV News, and “when Omicron first appeared in 2021, experts compared it to a monster”.

Mark Woolhouse, professor of Infectious Disease Epidemiology at Edinburgh University, told the site that “what they meant by that is it looks different from anything we’ve seen before”.

What are the symptoms?

The symptoms of XBB.1.5 recorded so far do not differ from those caused by other Omicron subvariants.

According to the NHS, Omicron symptoms include a high temperature or shivering; a new, continuous cough; change to taste or smell; head and body aches; a sore throat; a blocked or runny nose; tiredness; and gastric symptoms.