Here’s what you need to know about COVID’s XBB.1.5 ‘Kraken’ variant

The omicron offshoot’s ability to easily infect cells may be helping it spread rapidly in places

The omicron variant’s family tree has grown substantially over the last year. The brood now encompasses a subvariant soup with alphanumeric names such as BA.2, BA.5 and BF.7. The U.S. Centers for Disease Control and Prevention estimates that two versions — BQ.1 and BQ.1.1 — caused just over half of new infections in the United States during the week ending January 7.

Now, a newcomer dubbed XBB.1.5 seems poised for a rise to dominance. According to CDC estimates, it accounts for more than 80 percent of new cases in parts of the northeastern United States. For the week ending January 14, it was responsible for 43 percent of new cases across the country.

But while previous variants such as alpha, delta and the original omicron were linked to massive surges of new infections, it’s not yet clear whether XBB.1.5 is destined for a similar path. Preliminary evidence suggests the subvariant, nicknamed the Kraken in some circles, is more transmissible than its predecessors. That trait, however, is a hallmark of viral evolution — successful new variants must be able to outcompete their siblings.

For now, experts at the World Health Organization are keeping a close eye on XBB.1.5. But it’s too early to say whether it might take over the globe. Most cases currently come from the United States, the United Kingdom and Denmark.

Science News spoke with infectious diseases specialist Peter Chin-Hong of the University of California, San Francisco about the latest coronavirus variant to make headlines. The conversation has been edited for length and clarity.

SN: What is the difference between XBB.1.5 and earlier versions of omicron?

Chin-Hong: There are lots of variants that get produced all the time. It’s a normal thing for the virus as the virus makes more copies of itself. It’s not exactly precise or accurate, so it makes errors, [which are the variants]. It’s kind of like a bad photocopy machine in the office.

XBB, a sibling of XBB.1.5, was scary — and that was seen in the fall of 2022 — because it was one of the most immune-evasive variants around. But the reason why XBB never took off around the world — it was really in Singapore and India — was that it didn’t really infect cells quite as well.

XBB.1.5 has the immune slipperiness of XBB, but it also has this new mutation that makes it easy to infect cells. So it’s kind of like a bulldog in not wanting to let go of the cell. Whereas XBB was kind of invisible, like it had the invisibility cloak from Harry Potter, it didn’t have the bite. But XBB.1.5 has the invisibility cloak, plus the bite.

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