- The XBB.1.5 coronavirus variant is spreading quickly in the US — it's causing 40% of cases.
- This "kraken" variant is more transmissible and evades the immune system better than other Omicrons.
- It has a new mutation called F486P, that has "supercharged" the variant, one expert said.
A supercharged coronavirus variant called XBB.1.5 is spreading quickly in the US — and it's aggressive enough that scientists have nicknamed it the "kraken" variant.
"It's probably, arguably, in terms of its immune evasiveness and its ability to attach well, more formidable than any of the other subvariants currently around," Dr. John Swartzberg, an infectious disease expert and professor emeritus at the University of California Berkeley's School of Public Health, told Insider.
According to Centers for Disease Control and Prevention estimates, XBB.1.5 is now responsible for more than 40% of all COVID-19 cases nationwide — a dramatic climb from where it stood just a month ago, when it accounted for less than 4% of cases. In northeastern states including Connecticut and Vermont, XBB.1.5 has essentially taken over: it accounts for more than 75% of new cases.
"It's doing pretty well right now," computational biologist Andy Rothstein told Insider. "It's doubling week over week."
Rothstein, who helps lead the CDC's airport testing and sequencing program for Concentric by Ginkgo, a biosecurity division of the Boston-based biotech company Ginkgo Bioworks, said the XBB.1.5 variant has two things in its arsenal now that are giving it a competitive advantage: it is more contagious and more immune evasive than other versions of Omicron.
XBB.1.5 has some new mutational tricks
The XBB.1.5 variant is a descendant of XBB, which was a mashup of two different versions of BA.2 (what virus experts call a "recombinant variant"). Experts were worried about XBB as early as October, when it surged in Singapore, but it ended up fizzling out quickly there and scientists still aren't quite sure why.
XBB.1.5 was first noticed in the northeastern US around New York and Connecticut, and it has a few new mutational tricks up its sleeve.
Specifically, it has a new mutation called F486P, which has "supercharged" the variant, Rothstein said, allowing it to attach to ACE2 receptors in our body more easily. Practically, this could make the virus better at spreading and infecting us than the original XBB.
It's still unclear whether XBB.1.5 will completely take over in the US, like BA.5 did last summer, but Rothstein said there are a lot of signs suggesting the Omicron subvariant may become responsible for a large share of domestic cases in the near future, and, at the very least, it will probably co-circulate for a while with other variants.
We don't yet know if XBB.1.5 will cause more severe illnesses
It's still unclear whether XBB.1.5 will cause more virulent infections, making patients sicker than other Omicron variants we've seen before, Swartzberg said.
"The preliminary evidence is that it doesn't appear to make us that sick — it's not as bad as Delta was," he said. "It's more like the other Omicrons."
COVID-19 caseloads are decreasing both overall in the US and in the northeast where XBB.1.5 is most prevalent. Swartzberg called that a "wonderful shock" given the holidays, and all the indoor gathering that's been going on this winter. Though COVID-19 hospitalization rates are up slightly, those severe cases may not be reflective of XBB.1.5 — they are likely due to increases in disease spread we saw in mid-December, before the kraken variant was very prevalent.
"We're almost a victim of too much science in the sense that we can track these new variants really well, but we really don't know how to interpret them very well," Swartzberg said.
Vaccines still work decently against XBB.1.5
Preliminary data suggests the new, bivalent COVID boosters provide decent protection against XBB.1.5.
"It's not ideal, but it's better than it could have been," Swartzberg said. "Pretty good protection against XBB in terms of hospitalization and death. Probably not much of anything to preventing infection."
For now, the infectious disease expert's advice remains "the same as always," he said: Stay up to date on vaccinations (both flu and COVID), and wear a mask that fits you well like an N95 or KN95 whenever you're indoors in a public place.
"If you do those two things during the month of January and for much of February, you're going to not only protect yourself against the ravages of COVID, but also the other respiratory viruses that are circulating," he said.
His own plan is to keep masking up indoors in public "until the numbers of cases of COVID and other respiratory viruses dramatically drop, which I hope will be sometime in late February."