Get ready for the newest omicron COVID variant — Arcturus

SAN FRANCISCO  — The World Health Organization has elevated the fast-growing Omicron sublineage XBB.1.16 as a new variant of interest, and says it is outcompeting the previously dominant XBB.1.5 in many regions.

XBB.1.16 is a descendant of the recombinant XBB, which is a mashup of two BA.2 sublineages. On social media, the variant has been nicknamed Arcturus, like the brightest star in the northern celestial hemisphere. 

Currently, it is the dominant variant in India, where it is causing a wave of mostly mild illnesses. But it has been spotted in 32 other countries, including the United States.

This offshoot is very closely related to XBB.1.5. It has two gene changes that are different, including one in its spike protein, said Francois Balloux, director of the UCL Genetics Institute, at University College London, in a news release.

 Balloux said he expects it to do well in countries that didn’t have a sizable wave of cases caused by the XBB.1.5 sublineage, like China and India. He says he doesn’t expect it to have much impact on case numbers in the UK.

Studies have shown that whether a variant will cause a wave of cases in a country very much depends on the immunity in the population as well as the variant that was last the dominant cause of infections there.

WHO says that while this variant seems to be spreading faster than previous variants, and escapes immunity — even in people who’ve recently had the XBB.1.5 strain — it does not seem to be causing more severe illness. Therefore, WHO says the risk from this variant is low.

Last week in the United States, XBB.1.16 accounted for an estimated 10% of Covid-19 cases nationally, up from about 6% the week prior. The XBB.1.5 variant continues to be the dominant cause of new infections in the United States, according to data from the US Centers for Disease Control and Prevention.

WHO is recommending that countries share information about this variant, as well as conduct tests to see how well the immunity in their populations will defend against it. It’s also asking countries to keep an eye on certain indicators of disease severity as this sublineage spreads.