Omicron spawn XBB.1.5, also known as “Kraken,” now dominates the U.S. COVID variant scene, comprising about 61% of cases, according to federal health data released Friday.
But now there’s a new player tracked by the US Centers for Disease Control and Prevention who could give Kraken a run for his money. CH.1.1, or “Orthrus,” is estimated to have accounted for 1.5% of U.S. cases on Friday. Another offspring of Omicron, he was named after a mythical two-headed cattle dog slain by Hercules, by an Australian variant tracker mike honey.
Not much is known about the relatively new strain, whose levels have been rising globally since November. Like other “high-flying” COVID variants, it has the potential to be more transmissible, to evade immunity from vaccine and infection, and to cause more severe disease.
Additionally, he exhibits a disturbing mutation seen in the deadly Delta variant not usually seen in Omicrons, a mutation that could make him even more intimidating to an enemy. Although CH.1.1 is not a «deltacron» – a recombinant or a combination of Delta and Omicron – it is an excellent example of convergent evolution, a process by which variants of COVID evolve independently but pick up the same changes.
No one knows how CH.1.1 will play out in various countries around the world, including the United States, said Dr. Michael Osterholm, director of the Center for Infectious Disease Research and Policy (CIDRAP) at the University of Minnesota. Fortune.
«I don’t think we have a clear idea of which variants to be concerned about and which not to be,» he says.
Case in point: XBB.1.5, which «started to look like a very serious challenge, in terms of COVID» in the US. But after achieving dominance in the Northeast, «it just started to falter in the rest of the country,» where it hasn’t grown as quickly, he says.
«We’ve seen this before: what may seem like a difficult variation turns out not to be a real challenge.»
The bottom line, according to Osterholm: Anyone who thinks they can tell you what the future of the pandemic looks like — and make no mistake, we’re still in a pandemic, he says — “probably has a bridge to sell you.”
Lack of a crystal ball aside, here’s what’s known about the variant under World Health Organization scrutiny.
Where and when was it discovered?
CH.1.1 emerged in Southeast Asia this fall and is now responsible for more than a quarter of infections in parts of the UK and New Zealand, according to a preprint paper published last week by researchers from Ohio State University.
Its prevalence has risen sharply since November and now accounts for about 10% of COVID samples sequenced each day worldwide, according to epidemic.info, a community repository of COVID information.
The variant is among those monitored by the WHO, the international health organization said in a report on Wednesday.
In which countries was it located?
New Zealand currently sees the bulk of CH.1.1 cases, according to Outbreak.info. There, it is responsible for more than a third of the sequenced cases. Other hotspots include Hong Kong and Papua New Guinea – it comprises around a quarter of cases in each country. It is responsible for just under a fifth of cases in Cambodia and Ireland.
Why is this so concerning?
XBB.1.5 continues to be the most transmissible COVID strain to date, according to a January 19 report by variant tracker Cornelius Romer, a computational biologist at the University of Basel in Switzerland, and others. But CH.1.1 is worth watching, he says. Like XBB.1.5, it is highly transmissible, with levels doubling every two weeks or so.
CH.1.1 also binds well to ACE2 receptors, the site where COVID infects human cells, according to researchers at Ohio State. This means it has the potential to neutralize – at least partially – antibody immunity from previous infection and vaccination, as well as cause more serious disease. It may be able to outperform other competitive Omicron strains in these areas due to a concerning L452R mutation seen in Delta, but not usually in Omicron.
The Ohio State researchers used a lab-created version of CH.1.1 and examined how well serum from 14 healthcare workers – who had received between two and four doses of the original vaccine and the new Omicron booster – neutralized it. They found that the workers’ sera produced 17 times fewer antibodies against CH.1.1 than against BA.4 and BA.5.
CH.1.1 and another new variant, CA.3.1, are more immune than the XBB and BQ subvariants, the researchers wrote, calling the finding «astonishing».
How has it evolved?
CH.1.1 is a descendant of BA.2.75, a variant that was dubbed «Centaurus» this summer but eventually died out.
Most of the dominant COVID strains right now are descendants of either BA.5, which swept the world this summer, or BA.2.75. The «family» variant is important to note, experts say, because recent exposure to BA.2.75 or BA.5 – or one of their offspring – may offer temporary protection against infection from that family.
For example: if you were recently exposed to a BA.5 variant, you may be less vulnerable to new BA.5 variants for a while, but more vulnerable to BA.2.75 variants, and vice versa. (Note that XBB.1.5 is also a descendant of BA.2.75.)
But with COVID, there are exceptions to every rule, it seems: Japan just saw back-to-back BA.5 waves that sent deaths there skyrocketing to a pandemic high, Osterholm notes.
Will the new Omicron COVID reminder protect me?
The protection offered by the original COVID vaccine is waning, the Ohio State researchers wrote. They recommended the new Omicron booster but noted that it will offer less protection against CH.1.1 and CA.3.1 than against other variants like XBB and BQ.1.1.
This story was originally featured on Fortune.com
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