Highly contagious Corona variant Arcturus arrives

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Many people have long since forgotten about Corona. But the XBB.1.16 variant brings the virus back to mind. Arcturus is spreading rapidly.

Coronavirus variant XBB.1.16, also known as Arcturus, has caused infection numbers in India to rise 281 percent in 14 days. He said the death toll also increased by 17 percent during the same period. Vipin Vashishta, a pediatrician, researcher and member of the WHO vaccine group, warned on Twitter, “If Arcturus could succeed in breaking population immunity of Indians who have successfully withstood the onslaught of previous variants, then the whole world must be seriously worried!”

Now, whether there is cause for “alarm” is unclear. While some experts, such as German virologist Martin Stürmer, recommend watching developments “very closely” because of Arcturus, others already advise prudence. “There is no reason to panic,” the Times of India quotes the former head of India’s Corona Task Force, Randeep Guleria. He says there have hardly been any severe cases so far, and appropriate behaviour would curb the risk of contagion.

Nevertheless, XBB.1.16 has now reached 22 countries. These include the USA, Singapore, Australia, Japan, Great Britain, Italy, Denmark and Austria. The variant from the Omikron family has also been detected in Germany. In many cases, however, travellers from India have been identified as the source of the spread.

Arcturus is a recombination of Omicron subvariants. According to the “Deutsche Apothekerzeitung” (DAZ), it probably originates from BA.2.10 and BA.2.75 and has already evolved from them in many cases. XBB.1 and XBB.1.5 were already rampant worldwide. The latter has been the dominant variant in the USA since December. According to the World Health Organization (WHO), the XBB family is rising worldwide and has displaced the previously dominant BA.5 and BA.2 variants almost everywhere.

XBB.1.16 has numerous mutations at the spike protein already known from XBB.1.5. However, additional new ones are added in Arcturus. One of them is the S486P mutation. It causes the virus to bind even better to the ACE2 receptor and ensures that the virus can enter the human body’s cells even faster. This would make XBB.1.16 even more infectious than other variants. Until now, variant XBB1.5 was considered the fastest-spreading variant. Compared to it, the new variant XBB.1.16 should have a growth advantage of 140 percent, according to DAZ.

Arcturus has additional mechanisms that block the body’s immune response: According to Friedemann Weber, head of the Institute of Virology at the University of Giessen, XBB.1.16 has “several other changes in the genome that affect not only the spike protein but also the so-called ORF9b gene, which is involved in suppressing the interferon response.”

Interferons are messengers infected cells produce to warn other cells of the infection and initiate countermeasures. Sars-CoV-2 has several of these so-called interferon antagonists, and ORF9b has not been among the strongest. As a result, the variant could undermine the immune defences of vaccinated and recovered individuals, explaining the sharp rise in infection in India.

What role the three critical points play in the further development of the pandemic remains to be seen. According to molecular biologist Ulrich Elling of the Institute of Molecular Biotechnology (IMBA) in Vienna, another aspect could also be relevant: “Countries currently experiencing XBB.1.16 waves did not have an outstanding XBB.1.5 wave.” This includes India but also Singapore.

If that proves accurate and a large XBB.1.5 wave protects against an Arcturus wave, that would be a relatively good outlook for Austria. After all, XBB.1.5 dominated the infection scene here.