What is XEC?

XEC is a subvariant of the omicron family and a hybrid between two previously documented subvariants: KP.3 and KS.1.1.

"XEC represents a fairly minor evolution relative to the SARS-CoV-2 diversity currently in circulation, and is not a highly derived novel variant such as those that were granted Greek letters," like alpha, delta, and omicron, said Francois Balloux, a computational biologist at University College London and director of the UCL Genetics Institute.

The new subvariant was first detected in Germany and is currently spreading through Western Europe, said Elizabeth Hudson, regional chief of infectious diseases at Kaiser Permanente Southern California. According to Peter Chin-Hong, an infectious disease expert at the University of California, San Francisco, XEC may make up 13% of coronavirus samples in Germany and 7% of samples in Britain.

XEC has yet to spread much in the United States. According to CDC, KP.3.1.1, a descendant of the FLiRT subvariants, is currently the dominant strain of the coronavirus nationwide. For the two-week period ending in Sept. 14, KP.3.1.1 was estimated to comprise 52.7% of all coronavirus specimens.

By comparison, XEC isn't yet tracked on CDC's variant website and won't be until it makes up an estimated 1% or more of coronavirus cases nationwide by CDC's estimates. However, another estimate from the variant tracker GISAID indicates that XEC currently makes up 1.11% of coronavirus cases in the United States as of Sept. 15.

Could XEC cause a fall and winter surge?

Some experts say it's likely that XEC will eventually become the dominant variant in the United States.

According to Hudson, past surges have tended "to move from Western Europe to the East Coast to the West Coast of the U.S. So if this does take off more and more as we get towards the colder weather months, this probably would be the variant that will potentially take hold."

Eric Topol, director of the Scripps Research Translational Institute, said that XEC is "just getting started."

"And that's going to take many weeks, a couple months, before it really takes hold and starts to cause a wave," Topol said. "XEC is definitely taking charge. That does appear to be the next variant. But it's months off from getting into high levels."

Hudson agreed, saying that if XEC does take off, "probably we should start to see it more like November, December time. So like after Halloween — when the weather will probably get more reliably cool here, people start to go indoors more often — that's when we're more likely to see this potentially take hold."

However, experts noted that current COVID-19 vaccines, which are formulated to target similar variants, should still offer protection against XEC.

Balloux said that while XEC has a "slight transmission advantage" over other recent coronavirus variants, vaccines should still offer good protection.

XEC is a "recombinant variant of some of the other Omicron lineages that have been around for a while, and it does appear to be more immune evasive, giving it a transmissibility advantage in the population with the immunity that it has," said Amesh Adalja, from the Johns Hopkins Center for Health Security. "But it doesn't really change anything, just like the last variant didn't change anything, or the one before that, one before that, or the one before that."

"If this becomes a dominant variant, it will decrease the efficacy against infection of the updated vaccines, but the updated vaccines will still be durable against severe disease [and] hospitalization, and that's what is really the primary function of our current, first-generation COVID vaccines," Adalja added.

"I always have hope," Hudson said. "And if folks get vaccinated — this is the perfect time now to get vaccinated against flu, get the new COVID shot — we could potentially tamp down on what will certainly be another more typical fall-and-winter surge. But I think the jury is out in terms of how bad it is going to be." (Lin, Los Angeles Times, 9/23; Lee, Forbes, 9/17; Roberts, BBC, 9/18; Putka, MedPage Today, 9/18)

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