CDC now tracking subvariant XBB: 3 notes

The CDC has begun tracking omicron subvariant XBB, which is now estimated to account for 3.1 percent of U.S. cases. 

The strain is most prevalent in the Northeast, according to the CDC's variant proportion estimates for the week ending Nov. 26, where it accounts for more than 5 percent of cases in HHS regions 1 and 2 — which includes Connecticut, Maine, Massachusetts, New Hampshire, Rhode Island, Vermont, New York and New Jersey. 

Three notes: 

1. XBB is a recombinant of two other omicron subvariants: BA.2.10.1 and BA.2.75. The strain spurred a major wave in Southeast Asia. 

2. The variant is thought to be more evasive than the now dominant BQ.1 and BQ.1.1, though there has been no indication it is more severe. Early evidence indicates XBB carries a higher reinfection risk than other circulating omicron sublineages, according to the World Health Organization. 

"There has been a rapid rise in XBB, but it doesn't look like it's particularly more severe than other variants," Dr. Derek Smith, director of the center for pathogen evolution at the University of Cambridge in the U.K., told CBS News in an interview in late October. "It got our attention and then was prioritized, even though it was small numbers, because it had quite a number of substitutions different from the currently circulating viruses in the [receptor-binding domain], which meant that it might be an escape variant." 

3. The updated booster should offer some, "but not optimal protection," against XBB, according to Anthony Fauci, MD, outgoing director of the National Institute of Allergy and Infectious Diseases. When asked about booster effectiveness in a Nov. 22 COVID-19 briefing at the White House, Dr. Fauci said, "The protection is diminished multifold with XBB."

Compared to BA.4 and BA.4, booster protection levels go down with the BQ pair. "It goes down even more with XBB. It doesn't fall off the map, but it goes down," Dr. Fauci said. 

Health experts anticipate the U.S. will see an increase in COVID-19 cases in the winter months as a collection of omicron subvariants circulates, though they have remained optimistic it will be less severe than last winter's omicron surge. 


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