As the Omicron subvariant Kraken (XBB.1.5) climbs to 66% of new COVID-19 cases in the U.S., a newer subvariant may be challenging its reign: Orthrus (CH.1.1), named after Greek mythology's two-headed dog monster.

The World Health Organization (WHO) Epidemiological Update cites that Orthrus (lineage CH.1.1) is most prevalent among European countries. However, it has been detected in 66 countries, including the U.S., Thailand, India, China, and New Zealand, and based on its characteristics, has the potential to outpace its Omicron counterparts.

According to a recent preprint paper titled, Extraordinary Evasion of Neutralizing Antibody Response by Omicron XBB.1.5, CH.1.1 and CA.3.1 Variants, Ohio State University researchers found that all three subvariants exhibited increased fusogenicity compared to BA.2, correlating with enhanced S processing. Fusogenicity refers to the ability of a virus or a viral particle to fuse with a host cell membrane and enter the cell. S processing refers to the increased processing of the spike (S) protein of the virus, which is the key protein involved in the fusion of the virus with host cells.

The team of researchers tested how well antibodies generated by people vaccinated against Covid-19 could neutralize the Omicron XBB.1.5, 3 CH.1.1, and CA.3.1 variants and found that the CH.1.1 and CA.3.1 variants were "highly resistant to both monovalent and bivalent mRNA vaccinations." More troublesome, their study posits that CH.1.1 contains the mutation L452R that's seen in the Delta variant but not in Omicron, suggesting that CH1.1 may be more infectious and more dangerous than other Omicron strains.

It's important to note that Orthrus (CH.1.1) is not a "Deltacron"—a recombinant of Delta and Omicron— but rather a prime example of convergent evolution. This is when variants evolve independently but pick up the same mutations.

Convergent evolution can make it more difficult to track the spread of the virus, which can hinder efforts to control and contain the pandemic and make it more difficult to develop effective vaccines and treatments. It can also lead to rapid mutations in the virus as different strains evolve similar traits in response to similar environmental pressures.

The COVID-19 pandemic continues to pose a significant threat to global health and safety. Although we've made substantial progress in controlling the spread of the virus, we are still experiencing high levels of transmission and are grappling with ongoing challenges. It is important to continue implementing public health measures, such as wearing masks, practicing physical distancing, and getting tested, even if you're asymptomatic.