The 'Kraken' COVID subvariant: What to know about quickly rising omicron descendant

illustration shows a coronavirus particle with red spike proteins jutting out of a while viral capsule
A new version of the omicron variant has become more common in the U.S. in recent weeks. (Image credit: Matt Anderson Photography)

Editor's note: This page will be updated as new data about XBB.1.5 emerges.

A new flavor of the omicron variant of SARS-CoV-2, the virus that causes COVID-19, was identified in October 2022. In the past several weeks, it has steadily gained prominence in the United States. The subvariant is known as XBB.1.5 but has also been given the unofficial nickname "Kraken," after the mythical sea monster.

Here's what we know so far about XBB.1.5 so far.

Related: Most widely used COVID-19 vaccines and how they work 

How did XBB.1.5 emerge and where is it spreading?

Scientists first identified XBB.1.5 in New York state in October 2022, The New York Times reported

The subvariant stems from a broader branch of the omicron family tree known as "XBB," which emerged as a result of two earlier versions of omicron — BA.2.10.1 and BA.2.75 — swapping genes, according to the World Health Organization (WHO). These closely related omicron subvariants had the opportunity to swap genes when they infected the same person at the same time. 

From their two parents, XBB viruses gained mutations that helped them evade protective antibodies gained through prior COVID-19 infections and through vaccinations. But there was a tradeoff: XBB viruses simultaneously lost some of their ability to bind tightly to cells, a key step in infection, the New York Times reported. This may explain why other versions of omicron initially outcompeted XBB viruses.

However, as XBB viruses spread, they picked up new mutations and XBB.1.5, a.k.a. the "Kraken," was born. The Kraken harbors a mutation called F486P, which appears to restore the virus's ability to tightly latch onto cells, researchers reported Jan. 5 in research posted to the preprint database bioRxiv. (This research has not yet been peer-reviewed or published in a scientific journal.)

In a Jan. 4 news conference, WHO Director-General Dr. Tedros Adhanom Ghebreyesus reported that XBB.1.5 is "on the increase in the U.S. and Europe and has now been identified in more than 25 countries." Genomic data submitted to the open access database GISAID shows that U.S., U.K., Austria, Denmark, Canada, Israel and Germany have detected the most XBB.1.5 sequences so far, and that the subvariant remains relatively rare elsewhere. 

How easily does it spread?

Available evidence suggests that XBB.1.5 is the "most transmissible" omicron descendent yet detected, Maria Van Kerkhove, the WHO's COVID-19 technical lead, said at a news conference on Jan. 4, according to The New York Times. In the U.S., XBB.1.5 is beginning to gain dominance over other circulating omicron subvariants. 

In early December, the Kraken made up an estimated 2% of all COVID-19 cases in the U.S., The Washington Post reported. That figure jumped to 40% in the last week of December, STAT reported

The Centers for Disease Control and Prevention (CDC) have not yet analyzed all the data from early January 2023, but their current projections suggest that XBB.1.5 accounted for more than 27% of U.S. cases in the first week of the year. In the northeastern U.S., where XBB.1.5 was first detected and remains most common, the subvariant accounts for more than 70% of new cases, according to The Washington Post.

That said, nationwide, other flavors of omicron — namely BQ.1 and BQ.1.1 — were still circulating at comparable levels to XBB.1.5 during the first week of January, the CDC's projections suggest.

Is XBB.1.5 more likely to cause severe disease?

Scientists will need to see many weeks of hospitalization and death data before determining whether XBB.1.5 is more likely to trigger severe disease compared with earlier versions of SARS-CoV-2, the virus that causes COVID-19. 

As the U.S. experiences a nationwide surge in COVID-19 infections, "we're seeing hospitalizations have been notching up overall across the country," Dr. Barbara Mahon, director of CDC's Coronavirus and Other Respiratory Viruses Division, told NBC News. "They don’t appear to be notching up more in the areas that have more XBB.1.5," which hints that the subvariant isn't necessarily more likely to cause severe disease than its predecessors. 

How well do boosters and treatments work against XBB.1.5?

Early data suggests that the so-called bivalent boosters — the two recently updated boosters made by Moderna and Pfizer — offer decent protection against XBB viruses, despite the lineage's ability to evade antibodies, according to a Dec. 21 report in the New England Journal of Medicine

"Lab studies suggest that the bivalent vaccine is still effective in protecting against severe disease, though perhaps not as much against infection," Andy Pekosz, a professor of Molecular Microbiology and Immunology at the Johns Hopkins Bloomberg School of Public Health, said in a statement. "XBB.1.5 is derived from the omicron variant BA.2, and while the current bivalent vaccine was developed for the BA.5 variant, it has been shown to generate antibodies that recognize BA.2," he said.

"Things like boosters are always beneficial," Kristian Andersen, a professor in the department of immunology and microbiology who tracks coronavirus variants at the Scripps Research Institute, told The Washington Post. "Even if you get infected, you are expected to have less viral load, and you are expected to be able to transmit the virus less."

(Notably, as of Jan. 4, less than 16% of eligible U.S. residents had received a bivalent booster, the CDC reported.)

Palxovid, an oral antiviral pill used to treat COVID-19, will be effective at treating infections with XBB.1.5, The New York Times reported. The pill may not be prescribed to all COVID-19 patients, as it's not compatible with certain medications, Pakosz noted, "but overall, for the vast majority of people, Paxlovid is still a good drug to be prescribed if you get COVID-19."

Nicoletta Lanese
Channel Editor, Health

Nicoletta Lanese is the health channel editor at Live Science and was previously a news editor and staff writer at the site. She holds a graduate certificate in science communication from UC Santa Cruz and degrees in neuroscience and dance from the University of Florida. Her work has appeared in The Scientist, Science News, the Mercury News, Mongabay and Stanford Medicine Magazine, among other outlets. Based in NYC, she also remains heavily involved in dance and performs in local choreographers' work.

  • Redfour5
    They should have saved the name for a variant of "true" importance. And it appears that those may be a part of history at this point. This is simply another variant evolving away from virulence and toward more efficient transmission. That is the nature of pandemic organisms irrespective of the organism or the populations impacted be they human, avian or anteaters. And it is a dynamic where you have the organism AND you have the hosts...

    This particular one is of a type we are familiar with both physiologically and as a self aware species... This virus is moving inexorably toward that of a "common coronavirus" like the others we deal with as a species

    Yes, it is possible that for a short period of time you could see a more virulent variant, but it will not survive, because selective pressures will always be toward survival and any organism that selects otherwise as in killing hosts, will eventually lose out. And with the speed this variant adapts, that speed can be characterized easily by how often a new variant emerges, is detected and then spreads within the human population as quantified by a longitudinal percentage of all variants as placed upon an epi curve. Wait, there will be another soon.

    This simple generalizable rule, for this virus, has ramifications for vaccine development and use as a function of sub-populations impacted and clinical characteristics displayed that themselves are changing over time as the virus adapts and the hosts adapt synergistically. This is interesting though as this pandemic is the first where humanity has been completely aware of what it was dealing with, generally speaking, and had tools both non-pharmaceutical and vaccine based at a level to actively intervene in the spread. We will need to look at that a bit more closely in the future as it will have a direct impact upon future actions when humanity faces a less benign pandemic organism.