What is CH.1.1? Meet ‘Orthrus’, a new wildcard Omicron strain with a worrying Delta mutation

Omicron spawn XBB.1.5, also known as “Kraken”, now dominates the US COVID variant scene, accounting for an estimated 61% of cases, according to federal health data released Friday.

But there is now a new player being tracked by the US Centers for Disease Control and Prevention that could give Kraken a run for its money. CH.1.1, or “Orthrus,” was estimated to account for 1.5% of US cases as of Friday. Another Omicron spawn, it is named after a mythical two-headed cattle dog killed by Hercules, by an Australian variant of tracker Mike Honey.

Not much is known about the relatively new species, whose levels have been rising globally since November. Like other “high-flying” COVID variants, it has the potential to be more transmissible, evade immunity to vaccines and infections, and cause more serious illness.

In addition, it contains a concerning mutation seen in the deadly Delta variant not generally seen in Omicrons – one that could make it even more terrifying to an enemy. While CH.1.1 is not “Deltacron” – a recombinant or combination of Delta and Omicron – it is a good example of convergent evolution, a process where COVID variants evolve independently but pick up the same mutations.

It’s everyone’s best guess how CH.1.1 will play out in different countries around the world, including the US, 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 really have a sense of which variants to worry about and which not to,” he says.

Example: XBB.1.5, which was “starting to look like it was going to be a very serious challenge, in terms of COVID” in the US. of the country,” where it hasn’t risen as fast, he says.

“We’ve seen this before: what appears to be a challenging variant 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 .”

Aside from the lack of crystal ball, here’s what we know about the variant monitored by the World Health Organization.

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 United Kingdom and New Zealand, according to a preprinted paper released last week by Ohio State University researchers .

Prevalence has risen sharply since November and now comprises about 10% of COVID samples sequenced around the world each day, according to breakout.info, a community repository of COVID information.

The variant is one of the variants monitored by WHO, the international health organization said in a Wednesday report.

In which countries is it located?

New Zealand is currently seeing 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 – comprising about a quarter of the cases in each country. It is behind just under a fifth of cases in Cambodia and Ireland.

Why is it so concerning?

XBB.1.5 remains the most transmissible strain of COVID to date, according to a Jan. 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 portable, with levels doubling approximately every two weeks.

CH.1.1 also binds well to ACE2 receptors, the site where COVID infects human cells, according to Ohio State researchers. That means it has the potential to suppress, at least in part, the immunity of antibodies to previous infection and vaccination, and to cause more severe disease. It may be able to outperform other competing Omicron strains in these arenas due to a concerning L452R mutation seen in Delta, but generally not in Omicron.

The Ohio State researchers used a lab-made version of CH.1.1 and examined how well the serum of 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 evasive than XBB and BQ subvariants, the researchers wrote, calling the finding “amazing.”

How has it evolved?

CH.1.1 is a descendant of BA.2.75, a variant nicknamed “Centaurus” this summer, but ultimately failed to materialize.

Most of the dominant strains of COVID right now are descendants of BA.5, which took the world by storm this summer, or BA.2.75. The “family” variant is important to note, experts say, as recent exposure to BA.2.75 or BA.5 — or one of their spawns — may provide some 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, 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 caused deaths there to skyrocket to a full-blown pandemic high, Osterholm notes.

Will the new Omicron COVID booster protect me?

The protection afforded by the original COVID vaccine is diminishing, the Ohio State researchers wrote. They recommended the new Omicron booster, but noted that it offers less protection against CH.1.1 and CA.3.1 than against other variants such as XBB and BQ.1.1.

This story was originally on Fortune.com

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