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XBB: The New COVID-19 Variant Dominating In The US

The Omicron subvariant is behind the recent surge in cases.


Maddy Chapman


Maddy Chapman

Copy Editor and Staff Writer

Maddy is a Copy Editor and Staff Writer at IFLScience, with a degree in biochemistry from the University of York.

Copy Editor and Staff Writer

Omicron variant SARS-CoV-2 COVID-19

XBB is a subvariant of Omicron. Image credit: FOTOGRIN/

As COVID cases surge in China and other countries worldwide, yet another new variant is on the rise: XBB. A subvariant of Omicron, XBB emerged in India back in August and has since spread across the globe.

A large number of US COVID-19 cases are now caused by XBB and its cousin XBB.1.5. But what exactly is this variant, which experts have suggested “could be the new variant to watch out for ... in 2023.”?


What is XBB?

XBB is a subvariant of our old friend Omicron. According to the World Health Organization (WHO), it is “a recombinant of BA.2.10.1 and BA.2.75 sublineages”, meaning it contains genetic information from both versions of the virus.

 XBB.1.5, meanwhile, is a mutated version of XBB.

Early research in hamsters, which is yet to be peer reviewed, suggested XBB may have developed resistance to immunity and could be capable of evading antibodies, resulting in breakthrough infections. In October, the WHO echoed this, citing “early evidence pointing at a higher reinfection risk, as compared to other circulating Omicron sublineages.” 

“The current data do not suggest there are substantial differences in disease severity for XBB* infections,” they went on to say. Claims that the mortality rate of XBB is higher than that of the Delta variant, or that the new subvariant is more “toxic” have also been disproved.

Where has XBB been found?

Initially popping up last summer, XBB has gone on to cause surges of COVID-19 in parts of Asia, including India and Singapore

More recently, the strain has spread further afield: a total of 74 countries have reported incidences of XBB.1, according to These include Malaysia, Indonesia, China, and Pakistan. The variant has also reached Europe and the US, as well as Australia.

As of December 19, 2022, 8,638 sequences of XBB.1 had been detected worldwide, more than 1,500 of these in the US. Forty-three states have reported the subvariant.

For the week ending December 31, 2022, XBB itself accounted for 3.6 percent of total cases in the US. XBB.1.5, however, was responsible for 40.5 percent, according to the Centers for Disease Control and Prevention. The omicron subvariants are particularly dominant in the northeast of the country, where more than 75 percent of cases are linked to XBB.1.5.


Across the Atlantic, the new subvariants are less prevalent but appear to be on the rise. In the UK, around 4 percent of COVID cases were caused by XBB.1.5 for the week ending December 17, figures from the Sanger Institute show.


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