Omicron XBB.1.5: new Covid variant nicknamed ‘Kraken’ is ‘most transmissible yet’, WHO warns

A new subvariant of Covid has been branded “the most transmissible yet” by the World Health Organisation (WHO).

The latest Omicron strain, officially named XBB.1.5, has been spreading rapidly in the United States, with cases of the variant more than doubling in just a week.

The strain, which has been nicknamed ‘Kraken’, now accounts for more than 40% of Covid cases in America, according to recent data releases from the Centers for Disease Control and Prevention (CDC), and it has now been detected in the UK. Concern about XBB.1.5 is largely due to how quickly it is spreading in the US, but so far it appears to be as mild as previous Omicron variants.

Dr Maria Van Kerkhove, WHO’s technical lead for Covid, noted that the variant has spread to at least 29 countries and “is the most transmissible form of Omicron to date.”

She told a press conference on Wednesday (4 January): “We are concerned about its growth advantage in particular in some countries in Europe and in the US... particularly the Northeast part of the United States, where XBB.1.5 has rapidly replaced other circulating variants. Our concern is how transmissible it is… and the more this virus circulates, the more opportunities it will have to change.”

She added: “We do expect further waves of infection around the world, but that doesn’t have to translate into further waves of death because our countermeasures continue to work.”

In response to the rapid rise in XBB.1.5 cases in the US, Dr. Ashish Jha, the White House Covid-19 response coordinator, addressed concerns about the strain. He wrote in a Twitter thread: “What do we know? 1. More immune evasive? Probably yes. More than other Omicron variants. 2. More inherently contagious? Maybe. It binds more tightly to the human ACE receptor. Might affect contagiousness. 3. Is it more dangerous: We don’t know.

“So of course, the big question is… How much protection do vaccines or recent infections offer? What we currently know: If you had an infection before July OR your last vaccine was before bivalent update in September, your protection against an XBB.1.5 infection is probably not that great.

“We will soon have more data on how well vaccines neutralise XBB.1.5. But right now, for folks without a very recent infection or a bivalent vaccine, you likely have very little protection against infection.

“And for older folks, diminishing protection against serious illness. The new bivalent shot [vaccine] is your best protection against both infection and serious illness.”

‘One to watch out for’

The warning from the WHO comes after a leading UK health expert warned the new subvariant could be “one to watch out for” this year.

Tim Spector, founder of the ZOE Covid app and professor of genetic epidemiology at King’s College London, responded to the rising case numbers after US scientist Eric Topol said in a post on Twitter that the new strain is out-competing all other coronavirus variants, and urged the CDC to take note.

Mr Topol said that such rapid growth of a variant has not been seen since the original Omicron strain emerged a year ago and about 75% of confirmed cases in the northeast of the US are now reported to be XBB.1.5.

The XBB.1.5 variant is a mutated version of Omicron XBB, which was first detected in India in August last year, and it has since been found in at least 74 countries, according to outbreak.info which uses data from the Global Initiative on Sharing Avian Influenza Data (GISAID). The UK, China, India, Pakistan, Indonesia and Australia are among the countries where the variant has been detected.

Studies have found that the variant is capable of evading antibodies from previous Covid infection or vaccination, but it has not yet been listed as a variant of concern by the UK Health Security Agency (UKHSA).

Just 4% of all Covid cases in the UK were the XBB 1.5 variant, according to figures from Cambridge’s Sanger Institute for the week to 17 December, but Prof Spector warned that the strain could be “one to watch this year”.

Responding to Mr Topol’s tweet showing cases of XBB.1.5 had more than doubled in the US in a week, he wrote: “XBB could be the new variant to watch out for ..in 2023”.

‘Stay at home’ and ‘don’t visit vulnerable unless it’s urgent’

The warning about the new variant comes as the UKHSA has issued fresh advice urging people to stay at home if they feel unwell amid a rise in Covid, flu and Strep A cases.

Officials have said the NHS is facing “intolerable” pressures as it grapples with staff shortages and high demand exacerbated by flu and Covid, prompting more than a dozen NHS trusts and ambulance services to declare critical incidents over the festive period.

Patients are facing long waits for treatment and delayed ambulances, while thousands of beds are being taken up by medically-fit people who should not be there, according to health officials.

The Royal College of Emergency Medicine claims that somewhere between 300 and 500 people are dying each week as a result of delays and problems with urgent and emergency care.

Professor Susan Hopkins, chief medical adviser at the UKHSA, is now advising people who feel unwell to avoid going out and visiting vulnerable people unless it is urgent in a bid to minimise the spread of infection as winter illnesses are still circulating widely. The advice is part of the UKHSA’s back-to-school steps to help protect children and vulnerable people as pupils return to education after the Christmas break.

She said: “It’s important to minimise the spread of infection in schools and other education and childcare settings as much as possible. If your child is unwell and has a fever, they should stay home from school or nursery until they feel better and the fever has resolved.

“Helping children to learn about the importance of good hand hygiene is also key, so practise regular handwashing at home with soap and warm water. Catching coughs and sneezes in tissues then binning them is another simple way to help stop illness from spreading.

“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 unless urgent, or visit vulnerable people.”