A significant new subvariant of the coronavirus known as XBB.1.5 ­– or ‘the Kraken’ – could soon cause a major upsurge in UK case numbers.

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The highly transmissible XBB.1.5 subvariant ­– another offshoot of the Omicron SARS-CoV-2 virus variant – has been detected in 38 countries so far, including the United Kingdom.

Although the United States is currently the hotspot for the sub-variant (XBB.1.5 accounting for an estimated half of the country's coronavirus cases), the European Centre for Disease Prevention and Control (ECDC) predicts it will become the dominant form of coronavirus in Europe between February and March this year.

So far, just less than a tenth of the world’s XBB.1.5 cases have been identified in the UK. But many scientists, such as Prof Paul Hunter from the Norwich Medical School of the University of East Anglia, claim a large wave of COVID cases is imminent.

“All the signs are that this is going to cause a bigger wave than we saw in the summer of 2022,” he tells BBC Science Focus. “While infections are falling in the UK at the moment, I will expect that to reverse over the next few weeks.

Dr Jeremy Rossman, senior lecturer in virology at the University of Kent, adds: “A lot of scientists are concerned that we’re at a really high risk of another relatively severe wave. We just haven't seen this jump in transmissibility in quite a while.”

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Fortunately, there’s no evidence so far that XBB.1.5 can cause more serious disease than its processors. Yet some serious questions remain. Could the Kraken’s high transmissibility still cause a significant number of deaths? Why is it that XBB.1.5 can spread more easily? And will vaccines still work against it? We examine all below.

What is the Kraken XBB.1.5 sub-variant?

First identified in October 2022, XBB.1.5 is a new sub-variant of the globally dominant Omicron coronavirus variant.

To get a bit more technical, it’s a mix of other significant Omicron sub-variants. As signified by the X in its name, XBB.1.5 (and its ancestor XBB) came about through a recombination of sub-variants BA.2.10.1 and BA.2.75.

Now, it’s not just the mix of these previous sub-variants that makes XBB.1.5 such a problem – there are over 50 ‘X’ sub-variants that haven’t caused major concern so far. The main issue with XBB.1.5? Its spike proteins, which have mutated significantly.

“It’s a mutation that researchers previously identified and predicted – one that they said if any virus got would allow it to better bind with cells. And that is exactly what we're seeing right now,” says Rossman.

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Where exactly did this combination and mutation take place? Scientists aren’t sure. “A good guess might be somewhere in New York, where it really started to spread. But that is only a guess,” says Rossman.

Why is the XBB.1.5 variant called the Kraken?

In short: because we’ve run out of Greek letters.

In a bit longer: there are now so many types of Omicron (over 500 and counting), some scientists are now naming key sub-variants after mythological creatures to better speak about the virus’s ever-growing family tree.

Other Omicron subvariants deemed worthy of a name include BA.2.75 (the Basilisk), XBB.1 (Hippogryph) and BF.11 (Python).

What are the symptoms of Kraken COVID?

At present, there is nothing to suggest that the symptoms of infection with the new XBB.1.5 variant are different to other coronavirus strains.

The main symptoms of COVID-19, according to the NHS, are:

  • A high temperature – this means you feel hot to touch on your chest or back (you do not need to measure your temperature)
  • A new, continuous cough – this means coughing a lot for more than an hour, or three or more coughing episodes in 24 hours (if you usually have a cough, it may be worse than usual)
  • A loss or change to your sense of smell or taste – this means you've noticed you cannot smell or taste anything, or things smell or taste different to normal
  • Shortness of breath
  • Fatigue – feeling tired or exhausted
  • An aching body
  • A headache
  • A sore throat

How much more transmissible is XBB.1.5?

Scientists aren’t completely sure how much more transmissible XBB.1.5 is. But it is clear from initial data that the variant is spreading extremely quickly – the virus is growing at a rate 12 per cent faster than other types of coronavirus in the US.

The picture in the UK looks very similar. Although making up only 5 per cent of all coronavirus samples sequences in the last week of 2022, the UK Health Security Agency (UKHSA) now says that XBB.1.5 could soon become the most dominant strain of coronavirus in the UK.

The world, according to Rossman, could soon follow. “Unless a new variant comes along that can outcompete it, which is entirely possible, I do think that this sub-variant will soon be the most dominant around the globe,” he says.

Does the Kraken cause more severe disease?

Here is the good news. So far, there is no evidence so far that the XBB.1.5 makes people more ill than previous coronavirus variants.

Additionally, the World Health Organisation (WHO) has said that XBB.1.5 “does not carry any mutation known to be associated with potential change in severity”.

As Rossman adds: “You’re certainly more likely to catch XBB.1.5. But if you do catch it, there’s no evidence you’re more likely to end up in hospital or die from the virus than a few months ago.”

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Will our current vaccines work against XBB.1.5?

At the moment, there is very little data to be exactly sure, but the WHO says there are signs the variant could be one of the most “antibody-resistant variants to date”.

One preliminary study indicated that XBB.1 variants were up to 21 times more evasive against vaccine antibodies, compared to the variant dominant in the UK since June 2022 (BA.5).

Another study that has not been peer-reviewed suggests that people previously infected with the virus and who have received three or four doses of an mRNA COVID vaccine (such as Moderna or Pfizer) are still likely not to have the immunity needed to guard them against an XBB.1.5 infection.

“Even for people who have had the original vaccine and boosters, the protection from getting infected and having symptoms with XBB.1.5 is very poor,” says Rossman.

“The protection given by bivalent boosters [the second generation of vaccines, rolled out during autumn 2022 in the UK] is a little better. But it’s still dramatically reduced – some estimating the efficacy is only 30 per cent or less.”

However, while XBB.1.5 has reduced a jab’s protection from infection (and developing symptoms and long COVID), vaccines “still remain effective against severe disease”, according to the ECDC.

Could a new vaccine be made to combat XBB.1.5? It is possible a new generation of boosters could be produced, just like last year’s bivalent boosters. However, there are no current plans for its production.

Will a lateral flow test still detect XBB.1.5?

Like with other previous Omicron variants, our current lateral flow tests are still likely to detect the virus. However, highly-transmissible variants like XBB.1.5 may work so quickly in the body that you may take a lateral flow test after the point where the virus is detectable.

As Rossman explains: “It's not necessarily that the test can’t pick up the virus, but that sometimes if the virus replicates really fast – like this variant might – sometimes that means the whole infection process goes so quickly in you that you only have that peak of virus that's high enough to detect for maybe six hours.”

Unfortunately, a shorter infection time doesn’t necessarily mean the time you’re ill is any shorter. And while the infection time with highly transmissible variants is lower on average, this is only an average. It may take a week or longer before you exhibit symptoms and spread the virus, or it could take a day.

And this means, according to Rossman, lateral flow tests are still a vital tool. “They should still work and they are certainly worthwhile,” he says.

“If you’re worried, do repeat tests. And remember: if you get a negative test, it doesn’t mean there’s no chance you’re not infected.”

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So how dangerous is XBB.1.5?

At the moment, scientists think that XBB.1.5 isn’t more likely to cause serious disease in one individual, compared to previous variants. However, because XBB.1.5 is much more transmissible than the coronavirus variants we’ve seen before, there are fears it could spread to many more people. And with more people infected, there’s more chance a number of them could get seriously ill.

So, should we be worried about a large wave of XBB.1.5 cases? “Absolutely,” says Rossman. “Anything that makes the virus more transmissible can often lead to an increase in hospitalisations of vulnerable people. And even if there’s no change in the severity of the virus, more people could get sick.”

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There’s also the risk that an uptick in infections could overstretch the NHS, as Hunter explains: “I don’t think we’re going to see anything like the number of deaths from COVID compared to January 2022. But this is happening at the same time as we’ve got very high numbers of flu hospitalisations. It is a big concern and it could be very tough.”

For Rossman, it’s not just the new variant that’s a concern, but also people’s attitude towards the virus. “There’s been a huge sense of complacency emerging,” he argues. “Many people aren’t wearing masks in crowded areas. The uptake of booster vaccines has been low.”

He adds: “I see people wearing surgical masks. And these do help you from spreading the virus to other people, but they don’t really help protect yourself from the virus. And the more transmissible the virus gets, the less protection they offer. Instead, an FFP2 or FFP3 mask that fits well will filter out the virus, regardless of how transmissible it is.

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“We don’t need lockdowns or anything like that. But having an individual level of protection is still really important while this virus spreads.”

About our experts

Paul Hunter is a professor in medicine at the University of East Anglia’s Norwich Medical School. His research covers the epidemiology of emerging infectious disease, especially that linked to environmental factors. He has conducted epidemiological studies in the UK and around the world.

Jeremy Rossman is the honorary senior lecturer in virology at the University of Kent. His research focuses on the process of infectious disease outbreaks, and he has contributed to studies published in journals including PLoS Pathogens, Bioinformatics and Cell.

Authors

Thomas Ling
Thomas LingDigital editor, BBC Science Focus

Thomas is Digital editor at BBC Science Focus. Writing about everything from cosmology to anthropology, he specialises in astronomy and the latest psychology, health and neuroscience discoveries. Thomas has a Masters degree (distinction) in Magazine Journalism from the University of Sheffield and has written for Men’s Health, Vice and Radio Times. He has been shortlisted as the New Digital Talent of the Year at the national magazine Professional Publishers Association (PPA) awards. Also working in academia, Thomas has lectured on the topic of journalism to undergraduate and postgraduates at The University of Sheffield.

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