Could Omicron subvariant nicknamed 'the Kraken' bring a new Covid wave to UK?

A Omicron subvariant thought to be responsible for a rapid increase in US Covid cases has been detected in the UK.

In the US, XBB.1.5 is behind 40% of current infections.

We take a look at XBB.1.5, nicknamed 'the Kraken' in various media reports, and what impact it could have here in the UK.

What is Omicron XBB.1.5?

XBB.1.5 is a recombinant subvariant, meaning it was formed when fragments from two other variants merged.

Professor Mark Woolhouse, Professor of Infectious Disease Epidemiology, said: "It almost certainly means that it happened in the very rare instance when somebody was infected with two strains at the same time.

"The result was that the virus genomes could exchange with each other and they produced this new strain."

How does it differ from other Omicron subvariants?

According to Cambridge University's Professor Ravindra Gupta, a change to Omicron's spike protein makes XBB.1.5 better suited to escaping antibodies. The change also helps it to cling on to and enter cells.

Why has the subvariant been nicknamed 'the Kraken'?

The Kraken is a legendary octopus-like sea monster.

When Omicron first emerged in 2021, experts compared it to a monster, Professor Woolhouse noted.

"What they meant by that is it looks different from anything we’ve seen before,” he said.

What impact has XBB.1.5 had in the US?

Data from the US' Centres for Disease Control and Prevention (CDC) showed that by Saturday, the strain was behind 41% of cases.

The figure is up from 22% one week earlier and 4% one month earlier.

At 100,622,00, cases in the US aren’t “breathtakingly high”, Professor Woolhouse said. However, he noted that infections are increasing and "the increase does seem to be associated with this recombinant variant".

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Is Omicron XBB.1.5 more transmissible than the subvariants that came before it?

Experts think that, yes, it is more transmissible. Maria Van Kerkhove, Covid-19 technical lead at the World Health Organisation (WHO), said the rate XBB.1.5 spreads at is a "concern".

“The more this virus circulates, the more chances it will have to change,” she said, adding that further waves of transmission do not necessarily have to translate into more deaths, with the wide availability of vaccination and drugs.

Is the disease XBB.1.5 causes more severe?

Ms Van Kerkhove said there is no data yet to prove that XBB.1.5 causes more severe disease, but that WHO is working on a new risk assessment of the variant that it expects to release soon.

Professor Gupta notes that previous subvariants of Omicron were relatively mild, so "there’s no good reason why we might expect this one to be different".

Could the subvariant take off in the UK?

Figures for the week to Saturday 17 December from the Sanger Institute in Cambridge estimate that one in 25 Covid-19 cases in the UK were XBB.1.5.

However, the prediction was based on just nine samples, so the UK will have to wait for more data in the coming weeks to get a better picture.

Professor Paul Hunter, Norwich Medical School, University of East Anglia says its increase in the will "almost certainly" cause a surge of infections.

“For a variant to increase so rapidly [in the US] over less than four weeks would suggest a fairly substantial growth advantage," he added.