First Kraken, now Orthrus: What’s this highly transmissible COVID variant that US, China are tracking?

Monsters from Greek mythology are taking a new form – of COVID-19 variants. Now experts warn of Orthrus. Officially called CH.1.1, this Omicron spawn could leave the fast-spreading Kraken behind

FP Explainers February 02, 2023 12:39:07 IST
First Kraken, now Orthrus: What’s this highly transmissible COVID variant that US, China are tracking?

XBB.1.5, also known as Kraken, is the most dominant virus in the US right now. But experts warn that Orthrus could spread as quickly. AFP

Even as the war in Ukraine, the possibility of a US-China conflict, and global economic gloom catch our attention, the fight against COVID-19 is far from over. The coronavirus continues to mutate. There is the “Kraken” and now the “Orthrus”, both these Omicron subvariants get their names from monsters from Greek mythology. The United States and China are now desperately tracking the latter. Officially, it is called CH.1.1.

What do we know about “Orthrus”?

CH.1.1 is an Omicron spawn, which is now on the radar of the United States Centres of Disease Control and Prevention (CDC). Until last week, it comprised 1.5 per cent of cases in the country.

The most dominant virus in the US is the XBB.1.5, known as the Kraken. It accounts for more than 60 per cent of the cases, according to federal health data released on 24 January. But there is a growing fear that the Orthrus could leave the highly transmissible Kraken behind.

Orthrus is named after a mythical two-headed cattle dog killed by Hercules by Australian variant tracker Mike Honey, according to a report in Fortune.

Also read: Why the XBB variant is not deadlier than Delta

Where was the strain discovered?

CH.1.1 emerged in Southeast Asia and has been spreading globally since November. It has been detected in 66 countries and is responsible for about 10 per cent of COVID samples sequenced around the world every day, according to, which aggregates data across scientific sources.

Where has CH.1.1 spread?

The strain has been identified in more than a quarter of infections in parts of the United Kingdom and New Zealand, according to researchers at Ohio State University, the Fortune reports. It is also found in Papua New Guinea, Cambodia and Ireland. In Hong Kong, Orthrus is responsible for a quarter of cases.

China is also on the watch out. Around 24 cases of the transmissible subvariant have been reported from the mainland in three months, according to Chinese health authorities. However, they say it is unlikely to cause another wave.

“Despite an increased ability to resist immune responses and a higher transmissibility, which might increase breakthrough infection and reinfection risks, the population in China has a high level of neutralising antibodies,” the Chinese Centre for Disease Control and Prevention (CDC) said in a statement on Tuesday night, according to South China Morning Post (SCMP).

First Kraken now Orthrus Whats this highly transmissible COVID variant that US China are tracking

China experts say that it is unlikely that Orthrus could lead to another wave. AFP

Should we be concerned?

Like XBB.1.5, the Kraken, Orthrus is highly transmissible with levels doubling every two weeks. Variant tracker Cornelius Romer, a computational biologist at the University of Basel in Switzerland, said that CH.1.1 is worth keeping an eye on.

According to experts, Orthrus carries a mutation – L452R – which increases its immunity to current vaccines. This mutation is seen in Delta and not in Omircon, which raises the concern that it can outperform other competitive strains of the latter.

CH.1.1 binds well to ACE2 receptors, the site where COVID infects human cells, according to Ohio State researchers. That means it has the potential to override, at least partially, antibody immunity from prior infection and vaccination, as well as to cause more severe disease, reports Fortune.

Researchers said they found it “astonishing” that CH.1.1 and another new variant could evade immunity more easily than XBB and BQ subvariants.

However, China’s CDC says that the mutation found in CH.1.1 is present in subvariants like BA. 5.3 and BA. 5.1.3. It is unclear if it could cause more severe symptoms of the disease.

First Kraken now Orthrus Whats this highly transmissible COVID variant that US China are tracking

Hong Kong is one of the places where Orthrus has been detected. AFP

Do vaccines work?

Both XXB.1.5 and CH.1.1 are descendants of BA.2.75. The most dominant strains in the world today have either evolved from BA.2.75 or BA.5.

If you are exposed to one of the BA.2.75 variants, you are less vulnerable to its other spawns. So if you have been infected with the Kraken, you might have some immunity over Orthrus.

According to researchers, Orthrus is highly resistant to mRNA vaccines (Pfizer-BionTech and Moderna vaccines) and antibodies produced by earlier BA.4 and BA.5 infections.

The Ohio researchers have said that the protection offered by the original COVID vaccine is waning. For the US, it recommends the new Omicron booster but said it will offer less protection against this variant compared to XBB and BQ.1.1.

With inputs from agencies

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