The title of Arcturus as the most contagious corona variant is already in danger. “A new contender for dethronement is here – Acrux (XBB.2.3), arguably the fastest of the currently circulating XBB clan,” writes Indian expert Vipin Vashishta, pediatrician and researcher at Mangla Hospital and Research Center in Bijnor, India, and a member of the WHO Vaccine Group, on Twitter. Acrux would come with a highly immune-evading mutation – S:T478K from the deadly Delta variant.
Why is XBB.2.3 called Acrux?
The currently circulating XBB lines are getting nicknames due to mutations and traits (immune escape, ACE2 binding, etc.), growth advantage, and remarkable distribution. The new nickname system uses astronomical names to convey information about ancestry. The explains T. Ryan GregoryCanadian evolutionary and genomic biologist and Professor in the Department of Integrative Biology and the Biodiversity Institute of Ontario at the University of Guelph.
As to the background to the new system, the representatives of the “World Health Network“: “Astronomical names are numerous and can be mapped in a way that gives clues to variants that are not obvious with Greek letters or PANGO aliases.” So in the specific case of Acrux this means:
- Begins with AH = BA.2 ancestry
- The name contains an R in the name = a recombinant or a progeny recombinant.
Also good to know: The pronunciation of “Acrux” is with an A as in “space” and a U as in “trucks”.
What mutations does Acrux bring with it?
Acrux, XBB.2.3, hat Vashishta according to four defining mutations:
- Spike mutations: S:D253G and S:P521S
- ORF mutations: ORF1a:G2091S and ORF7a:A13V
- Beyond XBB.2, Acrux has spike mutations P521S and S486P
And Acrux also develops many offspring quickly, and one of its offspring, XBB.2.3.2, is considered to be the fastest. This one also has an interesting ORF1a mutation that has already appeared in several fast-growing lines.
Where is Acrux already common?
XBB.2.3 was sighted first in India (Karnataka) and then in the USA – the origin is somewhat unclear, writes the Indian expert Vashishta and points to the animated map by data visualizer Mike Honey there. It shows the spread of the Acrux variant around the world.
Singapore (26 percent) and India (22 percent) are still the hotspots, Vashishta explains. Spain (11 percent) and Australia (8 percent) have also recently seen growth. Acrux has been seen in many other countries including Japan, South Korea, China, the UK and the US. In Asian countries, however, the newly documented subline in China is part of a whole bouquet of XBBs such as XBB.1.5, XBB.1.16, XBB.1.9, which currently dominate here.
In India, the share of XBB.2.3 is increasing, but it is still not able to displace the currently dominant Arcturus, according to the medic. However, its descendant XBB.2.3.2 might have an advantage.
How dangerous are the XBBs?
Even if the corona virus mutates continuously, the danger does not change at the same time. So far, there hasn’t been any evidence of a more disease-causing ability for any of the XBB variants, which includes both Acrux and Arcturus, compared to their predecessor lines. While the World Health Organization (WHO) has classified XBB.1.16 as a variant of interest (VOI), it writes: “The global risk assessment for XBB.1.16 is low compared to XBB.1.5 and the other variants currently in circulation, at this time and with available evidence.”
Growth advantages and immune escape properties have been observed in different countries and in different immune backgrounds, but no changes in severity have been reported. A slight increase in bed occupancy was recorded in India and Indonesia. However, the levels are much lower than previous variant waves.
Even experts in this country did not expect an increased burden of disease from XBB.1.16. “I don’t think that Arcturus will lead to many severe courses again,” said Ulf Dittmer, Director of the Institute for Virology at the University Hospital in Essen, when asked by FOCUS online.
In particular, people who have been vaccinated first and are then mildly to moderately ill have a very broad immunity – through antibodies as well as through T-cells. That applies to a lot of people in Europe. “This protects them very well against serious illness and no conceivable variant can completely avoid it.”