Experts are eyeing the new Omicron strain XBB.1.5—dubbed "Kraken" on the Twitterverse—for its potential to cause the next major COVID wave, thanks to its "escape strain" properties and ultra-high transmissibility.
The World Health Organization's technical advisory group on virus evolution is working on a risk assessment on the variant—the most transmissible yet, Maria Van Kerkhove, technical lead for COVID-19 response at the World Health Organization, said at a Wednesday news conference.
The organization has asked the U.S. Centers for Disease Control and Prevention to also report on the risks of the new variant, since XBB.1.5 was first identified in the U.S. and has “rapidly replaced other variants” in the northeastern part of the country, Van Kerkhove added.
Both reports are expected in the coming days. Right now, experts are predominantly concerned with Kraken's ability to quickly spread and overtake other strains of Omicron. In early December, it was a mere blip on the CDC's radar. As of Friday, it comprised an estimated 41% of cases nationally, positioning itself to become the dominant U.S. COVID variant after beating back the most recent wave of BQ variants.
Researchers are looking into whether Kraken might have other concerning properties, like the ability to cause more severe disease. So far, there is no evidence of this, according to Van Kerkhove.
What is known, however, is that Kraken is continuing Omicron's legacy of spawning variants that spread—and evade immunity from prior infection and vaccination—with increasing ease. Here's what we know so far about the latest Omicron spawn to make headlines.
When and where was Kraken discovered?
While it's only recently taken off globally, XBB.1.5 has been around for a while. It was first detected, in the U.S., on Oct. 22, according to the European Centre for Disease Prevention and Control (ECDC).
Where did it come from?
XBB.1.5 is a "recombinant"—or combination—of two spinoffs of Omicron BA.2, which was known as "stealth Omicron" for its ability to produce false negatives on some tests.
What countries are seeing it?
So far, the U.S. is seeing the lion's share of the new variant, according to the ECDC. This week, the CDC projected that it comprised around 75% of infections in regions 1 and 2, which include Connecticut, Maine, Massachusetts, New Hampshire, Rhode Island, Vermont, New York, New Jersey, Puerto Rico, and the U.S. Virgin Islands. Nationally, it was projected to be behind 41% of cases.
Some European countries are also seeing a steep rise in levels of Kraken, according to the WHO. The variant has so far been reported in 25 countries, which include Denmark, France, Austria, Netherlands, Germany, Italy, Spain, Sweden, Iceland, Belgium, Czechia, Portugal, and Ireland, according to the ECDC.
Why is it so concerning?
Right now, experts are focused on the variant's growth advantage over other strains of Omicron. In the U.S., XBB.1.5 was projected to comprise just around 1% of cases in early December. A month later, it's projected to be behind 40% of cases, and rising.
Kraken is estimated to have a growth advantage over other Omicron variants of 139% in North America, and 137% in Europe, the ECDC said in a Jan. 5 report, adding that the estimates come with "significant uncertainty." The organization reports an estimated doubling time of nine days, and said the variant was likely to be dominant in the U.S. when the CDC's new COVID forecast is released Friday.
Even if the variant becomes dominant in the U.S., it may not in Europe, the report points out, as "major differences in variant circulation have been observed between North American and Europe several times during the pandemic." Overall, Kraken is present in Europe at "low levels," and is therefore unlikely to contribute to an uptick in cases there this month, the report added.
Aside from being the most transmissible COVID variant yet, XBB.1.5 also binds extra well to the cells it infects, according to WHO officials. This quality allows a virus to replicate easily in a host, which could lead to more severe disease. But so far, there is no evidence of this, WHO officials said Thursday.
Is it causing hospitalizations and deaths to rise?
The jury is still out on this. The Northeast U.S., where XBB.1.5 is thriving, is seeing an increase in hospitalizations, Van Kerkhove said. And on Thursday the WHO reported a 20% increase in global COVID deaths over the past month. But it's unknown what factors are behind the trends, according to Van Kerkhove. Both upticks could be due to increased COVID spread that generally occurs around holidays, due to indoor gatherings, and are not necessarily indicative of a new, more problematic strain.
