Dec 31, 2022 - Health

What we know and don't know about the XBB.1.5 COVID subvariant

Covid surrounded by question marks.

Illustration: Aïda Amer/Axios

The XBB.1.5 COVID-19 subvariant — a new version of the Omicron variant — is sweeping through the United States right now amid a chaotic travel season and the early days of winter.

Why it matters: Cases tied to the new variant nearly doubled over the last week, according to estimates from the Centers for Disease Control and Prevention. And that's stoked fears that more cases could be on the way nationwide.

XBB.1.5 COVID subvariant: What we know

The XBB.1.5 strain is responsible for 40.5% of confirmed U.S. cases for the week ending on Dec. 31, the CDC estimates show. That’s up about 20% from the week ending on Dec. 24.

  • The XBB.1.5 variant is responsible for about 75% of confirmed cases in the Northeast alone, which includes New England, New Jersey and New York, the CDC estimates.

What they’re saying: "We're projecting that it's going to be the dominant variant in the Northeast region of the country and that it's going to increase in all regions of the country," Dr. Barbara Mahon, director of the CDC's proposed Coronavirus and Other Respiratory Viruses Division, told CBS News.

  • Mahon told CBS that the CDC did not list the XBB.1.5 lineage in earlier projections because it did not meet a minimum threshold set by the agency.

Zoom out: Experts have become increasingly concerned about the XBB.1.5 and XBB variants — recombinants of the BA.2 subvariant — in recent weeks after it popped up in multiple Asian countries, per Reuters. And it's spreading as China is seeing a massive surge of cases right now.

  • "Ironically, probably the worst variant that the world is facing right now is actually XBB," Dr. Michael Osterholm, an infectious disease expert at the University of Minnesota, told Reuters.

XBB.1.5 is different than the XBB variant because it can attach itself better to cells, CNBC reports.

  • “The virus needs to bind tightly to cells to be more efficient at getting in and that could help the virus be a little bit more efficient at infecting people,” Andrew Pekosz, a virologist at Johns Hopkins University, told CNBC.

XBB.1.5 COVID variant: What we don’t know

It’s unclear where this version of the Omicron variant came from, but it is spreading quickly.

  • We also don't know how fast and far it will spread. But John Moore, a professor of microbiology and immunology at Weill Cornell Medical College in New York, told Reuters he expects cases to peak in mid-January.
  • It's also unclear if there are specific symptoms tied to the new variant.

Symptoms and the XBB.1.5 COVID subvariant

There do not appear to be any additional COVID-19 symptoms tied to XBB.1.5 that are different than normal symptoms.

  • "There's no suggestion at this point that XBB.1.5 is more severe," Mahon, of the CDC, told CBS News.

Yes, but: Scientists said the XBB.1.5 variant has mutations that could allow the virus to evade COVID-19 vaccine boosters and cause more breakthrough infections, CNBC reports.

  • In October, the XBB subvariant was deemed best suited to evade COVID-19 immunity, Axios’ Erin Doherty writes.

What's next: "I think it is a really good time for people to do the things that we have been saying for quite a while are the best ways to protect themselves," Mahon told CBS.

More from Axios:

U.S. to require negative COVID-19 test for air travelers from China

Most Americans don't have peak protection against COVID

China sees more deaths as COVID "tsunami" takes hold

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