Coronavirus variant XBB.1.5 rises in the United States. A new year means a change. Just as scientists were starting to understand the alphabet soup of SARS-CoV-2 variants that are circulating around the world (like BQ.1.1, CH.1.1, and BF.7), a strange new mutation seems to be pushing one lineage to the top. Coronavirus variant XBB.1.Thank you for reading this post, don't forget to subscribe!
According to projections from the US Centers for Disease Control and Prevention (CDC) in Atlanta, Georgia, around 28% of US COVID-19 cases are now XBB.1.5 subvariant, and its prevalence is growing around the world. In the Northeast of the U.S., it seems to have quickly beaten out the many other immunity-avoiding variants that were expected to be around this winter. Coronavirus variant XBB.1.
“It will almost certainly take over the world. Now, I can’t find any competitors. “Everything else is different,” says Yunlong Cao, an immunologist at Peking University in Beijing whose team is studying the properties of XBB.1.5 in the lab.
Scientists warn that it is still not clear how XBB.1.5 will affect the United States and the rest of the world. In many countries, the variant might not cause a big rise in infections or hospitalizations because people have built up a lot of immunity from being exposed to earlier waves of COVID-19 and getting vaccinated, especially recent booster shots for people who are most likely to get sick from it.
Researchers say it will be important to keep a close eye on the lineage even if XBB.1.5 doesn’t cause big COVID-19 waves. The subvariant has a rare mutation that could make it more contagious and give evolution a chance to make more progress. Coronavirus variant XBB.1.
As its name suggests, XBB.1.5 is a branch of XBB, which is a type of SARS-CoV-2. This lineage is made up of two offspring of the BA.2 lineage, which started to spike in the early part of 2022. BA.2 is a branch of Omicron. The spike protein in XBB has a number of changes that make it better at avoiding antibodies. In the last few months, this has made XBB more common, especially in Asia, where it caused a rise in cases in Singapore. Coronavirus variant XBB.1.
Late in 2022, people who keep track of variants found out about XBB.1.5 because the spike protein had a rare amino acid change called F486P. Experiments done in Cao’s lab show that the mutation makes it easier for the variant to attach to the human ACE2 receptor, which is what SARS-CoV-2 uses to get into cells1. Importantly, the mutation doesn’t seem to change how well XBB can hide from antibodies. The results were put on the bioRxiv preprint server on January 5, but they haven’t been reviewed by other scientists yet. Cao says, “XBB really stinks at ACE2 binding,” and the F486P change in XBB.1.5 helps to make up for that.
Jesse Bloom, an evolutionary virologist at the Fred Hutchinson Cancer Center in Seattle, Washington, says there isn’t a clear link between a variant’s ability to attach to ACE2 and its ability to spread. “F486P seems to have given XBB.1.5 another boost, which is helping the virus spread,” he says.
A common variant in the United States.
The CDC says that XBB.1.5 is the second most common variant in the United States. It makes up 28% of cases nationally and up to 70% in the northeast (see “New year, new variant”). Moritz Gerstung, a computational biologist at the German Cancer Research Center in Heidelberg, thinks that the number of cases of the variant doubles about once a week in the U.S. and a bit more slowly in other places where it has been found. That’s about the same rate as the BQ.1 and BQ.1.1 variants in September 2022, but slower than earlier Omicron waves. “The speed with which XBB.1.5 spreads is still very fast,” says Gerstung.
Gerstung says it’s not clear if this growth will continue or if the variant will cause a lot more infections. BQ.1 and BQ.1.1 looked like they were going to make big waves, but in Europe and North America, they ran out of steam. If the same thing happens with XBB.1.5, the lineage could end up replacing other variants without causing a big rise in cases in some countries.
Version for cities
Jennifer Surtees, a biochemist at the University at Buffalo in New York, wonders if researchers are overestimating the growth of XBB.1.5 in the Northeastern United States. The variant is becoming more common in the sequences that her team works on in western New York, but she hasn’t notice yet that the number of XBB.1.5 genomes being record in labs in New York City is going up like a rocket.
Due to the drop in testing for COVID-19, it might not be easy to figure out how XBB.1.5 will affect things. Surtees adds. “I think that right now we are really flying blind. We don’t know how many real cases are out there.”
Tulio de Oliveira, a bioinformatician at Stellenbosch University in South Africa, thinks that the best way to measure XBB.1.5’s effect is to look at hospital cases and other ways to measure how bad a disease is. He says that a cold snap in the Northeastern United States and holiday parties could be part of the reason why the variant seems to be on the rise. “I think that a lot of scientists draw conclusions and make predictions too quickly and with too little information.”
Researchers agree on one thing: XBB.1.5, like its predecessor XBB, is a master at avoiding the immune system. It has a lot of mutations in its spikes that make the antibodies made by vaccinations and infections, including earlier Omicron strains, less effective. In lab tests2,3, bivalent vaccines increase the amount of antibodies that can stop an XBB infection (and probably an XBB.1.5 infection as well), but not by much, says Cao.
Researchers, like Cao, watched as Omicron lineages picked up a series of mutations in the viral spike protein that made it resistant to antibodies. This made it possible for new lineages to beat immunity from vaccines and previous waves. Because of the F486P mutation, XBB.1.5 is much more likely to spread than other circulating variants. However, there isn’t much pressure on the lineage to change right now, says Cao.
But XBB.1.5 won’t stay the same as global immunity to the subvariant builds, he says. “We will see a lot of new mutations that we have never seen before. Coronavirus variant XBB.1.