New omicron strain now makes up 40% of US cases: 3 notes

In one week, the prevalence of XBB.1.5 — an offshoot of omicron subvariant XBB — more than doubled in the U.S., according to the latest CDC estimates. 

CDC data suggests the highly evasive strain accounted for 21.7 percent of COVID-19 cases for the week ending Dec. 24, rising to nearly 41 percent as of Dec. 31. The new variant of concern is most prevalent in the Northeast, where it accounts for more than 70 percent of cases across HHS regions that include New England and New York. 

Two more things to know: 

  1. XBB.1.5 is a relative of XBB, a recombinant of two other omicron variants: BA.2.10.1 and BA.2.75. Last fall, XBB spurred a wave of infections in Southeast Asia, with evidence indicating the strain is more immune evasive than the BQ subvariants. Experts said that while XBB.1.5 is not more evasive than XBB, it has a growth advantage over other XBB strains due to a mutation that allows it to more effectively bind to cells, CNBC reported. 


  1. There is no evidence that XBB.1.5 causes more severe disease than other omicron strains. "We're seeing hospitalizations have been notching up overall across the country," Barbara Mahon, MD, director of the CDC's division on the coronavirus and other respiratory viruses, told NBC News. "They don't appear to be notching up more in the areas that have more XBB.1.5," she said. The daily average for COVID-19 hospitalizations in the U.S. was nearly 45,000 as of Jan. 2, up 8 percent over the last two weeks, according to HHS data compiled by The New York Times. 

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