New corona variant is spreading rapidly in the US – three points on XBB.1.5

It is disturbing news that WHO corona specialist Maria Van Kerkhove spread in Geneva on Wednesday. The Corona variant XBB.1.5 has already been detected in 29 countries and is spreading at a rapid pace, especially in the US. This development did not come as a complete surprise, as the past shows.

On October 27, WHO published its findings on the omicron subvariants BQ.1 and XBB, which were observed as “variants of concern”. Both variants are descendants of the BA.2 variant, which is still dominant worldwide.

XBB was more common in sequencing but could not be specifically linked to an increase in cases in October, according to the WHO. However, early studies indicated that the risk of reinfection was higher compared to other omicron variants. Meanwhile, BQ.1 slowly began to assert itself against other Omokron variants. The WHO therefore called on countries to closely monitor the XBB and BQ.1 variants.

As early as September it became clear that BQ.1 was likely to spread further. Cornelius Römer, who studies the spread of the coronavirus at the University of Basel, predicted in early October that BQ.1.1 would trigger a “wave of variants” in North America and Europe.

He was partially right. A month later, BQ.1 and its subvariants accounted for 30 percent of all cases in Switzerland and 17 percent in the US.

What Römer did not yet know was that the then inconspicuous XBB.1.5 variant would prevent the dominance of the BQ.1 variant. At the beginning of November it was only 0.1 percent in the US.

By mid-December, however, XBB.1.5’s share had already risen to 9.9 percent and doubled to 21.7 percent the following week. At the end of December, XBB.1.5 accounted for 40.5 percent of all cases in the US. This reduced the spread of BQ.1 again.

This visualization shows how fast XBB.1.5 has already spread:

Now the big question arises: how dangerous is XBB.1.5?

To answer this question, it is worth taking a look at the composition of the virus variant. It seems irritating at first that the XBB.1.5 variant, as a descendant of the BA.2 variant, doesn’t also start with the letter “B” – like, say, the BQ.1 variant. There’s a good reason for that.

XBB is the result of a so-called recombination of two BA.2 variants. This means that a person has been infected with both variants at some point, resulting in the combined variant.

This illustration by epidemiologist Emma Hodcroft illustrates this:

The “X” at the beginning of the name means it is a recombinant virus variant.

The reason why XBB was put under WHO surveillance in October was because of its significant immune escape properties. In other words, XBB is particularly resistant to antibodies from vaccination or previous infection. Why didn’t XBB or XBB.1 (the ancestors of XBB.1.5) prevail?

XBB possesses a higher immune escape but no higher transmissibility. In this case, the higher immune escape reduced the ability of the virus to infect human cells, virologist Wendy Barclay explains to “BBC”. Something that changed with the XBB.1.5 descendant. The fifth offspring of XBB.1 has a mutation that compensates for this “weakness”. This allows the virus to better evade the immune system AND infect cells more easily.

As a result, XBB.1.5 now not only displaces the prevalent variants, but also drives up the number of cases.

It is not yet known whether XBB.1.5 also causes serious illnesses. Virologist Barclay’s concerns are still limited as there is still no evidence that XBB.1.5 breaks vaccine protection against more severe courses.

In the US, the new variant leads to a significant increase in hospital admissions. However, it is not known whether the infected persons admitted were vaccinated or belonged to a risk group.

Against this background, the problem with XBB.1.5 at the moment is that due to rapid spread, there are many staff shortages in the population. A problem that has led to store closures and delivery delays in the past.

Two weeks ago, XBB.1.5’s share in Europe was still one percent. In Switzerland, the variant is not yet in the corona dashboard of the Federal Office of Public Health (BAG).

The WHO is currently working on a risk analysis, which should be published soon.