Editor’s note: This page will be updated as new data on 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. Over the past few weeks, it has steadily gained prominence in the United States. The sub-variant 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: The most widely used COVID-19 vaccines and how they work
How did XBB.1.5 originate and where is it spreading?
Scientists first identified XBB.1.5 in New York State in October 2022, The New York Times reported (opens in a new tab).
The sub-variant comes from a larger 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 – exchanging genes, depending on the World Health Organization (opens in a new tab) (WHO). These closely related omicron subvariants had the ability to swap genes when they infected the same person at the same time.
From both parents, XBB viruses acquired mutations that helped them evade protective antibodies acquired in previous 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 supplanted XBB viruses.
However, as the XBB viruses spread, they detected new mutations and XBB.1.5, aka the “Kraken”, was born. The Kraken harbors a mutation called F486P, which appears to restore the virus’s ability to lock tightly to cells, researchers reported Jan. 5 in research published in the Preprint Database. bioRxiv (opens in a new tab). (This research has not yet been peer reviewed or published in a scientific journal.)
In a January 4 press conference (opens in a new tab)WHO Director General Dr. Tedros Adhanom Ghebreyesus (opens in a new tab) reported that XBB.1.5 is “on the rise in the United States and Europe and has now been identified in over 25 countries”. Genomic data submitted to open access database GISAID (opens in a new tab) shows that the US, UK, Austria, Denmark, Canada, Israel, and Germany have detected the most XBB.1.5 sequences so far, and the subvariant remains relatively rare elsewhere.
How easily does it spread?
The available evidence suggests that XBB.1.5 is the “most transmissible” omicron descendant ever detected, Marie Van Kerkhove (opens in a new tab), the WHO’s COVID-19 technical lead, said at a press conference Jan. 4, according to The New York Times. In the United States, XBB.1.5 is beginning to dominate the other omicron subvariants in circulation.
In early December, the Kraken accounted for about 2% of all COVID-19 cases in the United States, The Washington Post reported (opens in a new tab). This figure rose to 40% in the last week of December, STAT reported (opens in a new tab).
The Centers for Disaster Control and Prevention (opens in a new tab) (CDC) have not yet analyzed all of the data from early January 2023, but their current projections suggest that XBB.1.5 accounted for more than 27% of cases in the United States during the first week of the year. In the northeastern United States, where XBB.1.5 was first detected and remains the most common, the subvariant accounts for more than 70% of new cases, according to the Washington Post.
That said, nationally, other flavors of omicron – namely BQ.1 and BQ.1.1 – were still circulating at levels comparable to XBB.1.5 during the first week of January, according to projections from the CDC.
Is XBB.1.5 more likely to cause serious illness?
Scientists will need to look at several weeks of hospitalization and death data before determining whether XBB.1.5 is more likely to trigger severe disease compared to earlier versions of SARS-CoV-2, the virus that causes COVID-19.
As the United States experiences a national increase in COVID-19 infections, “we are seeing hospitalizations have increased across the country.” Dr. Barbara Mahon (opens in a new tab)director of the CDC’s Coronavirus and Other Respiratory Viruses Division, said BNC News (opens in a new tab). “They don’t seem to increase more in areas that have more XBB.1.5,” suggesting 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 — both 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 (opens in a new tab).
“Laboratory studies suggest that the bivalent vaccine is still effective in protecting against serious illnesses, but perhaps not as much against infections,” Andy Pekosz (opens in a new tab)professor of molecular microbiology and immunology at the Johns Hopkins Bloomberg School of Public Health, said in a statement (opens in a new tab). “XBB.1.5 is derived from the omicron BA.2 variant, and although the current bivalent vaccine was developed for the BA.5 variant, it has been shown to generate antibodies that recognize BA.2,” a- he declared.
“Things like boosters are always beneficial,” Christian Anderson (opens in a new tab), 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 are infected, you are expected to have less viral load and less ability to transmit the virus.”
(Notably, as of January 4, less than 16% of eligible U.S. residents had received a bivalent booster, the CDC reported (opens in a new tab).)
Palxovid, an oral antiviral pill used to treat COVID-19, will be effective in treating infections with XBB.1.5, The New York Times reported. The pill may not be prescribed to all COVID-19 patients, as it is not compatible with certain drugs, Pakosz noted, “but overall, for the vast majority of people, Paxlovid is still a good drug. to prescribe if you contract COVID-19.”
