New COVID-19 Variant XBB Gaining Ground Among Americans

MONDAY, Nov. 28, 2022 (HealthDay News) -- U.S. health officials are tracking a new COVID-19 variant that is a combination of two earlier omicron subvariants. Known as XBB, this latest subvariant now represents 3.1 percent of new COVID-19 cases throughout the United States and 5 percent of cases in the Northeast.

Based on preliminary estimates from the U.S. Centers for Disease Control and Prevention, cases of XBB may be doubling every 12 days. However, the variant should not pose the same threat that the emergence of omicron posed a year ago, CBS News reported.

Surges have mostly been "driven by seasonality, people coming inside, spending more time around one another," but they have not specifically been driven by the emergence of a new variant, Ian Williams, Ph.D., deputy director of the Center for Preparedness and Response at the CDC, told advisers earlier this month, CBS News reported.

XBB appears to have emerged from the BA.2.10.1 and BA.2.75 omicron subvariants. Along with other omicron sublineages, it appears to be replacing BA.4 and BA.5, subvariants that spread widely this past summer. Now, BA.5 is responsible for fewer than 20 percent of new infections and BA.4 has become almost nonexistent, CDC data show.

Still, the panic button does not need to be pushed, experts said. "There has been a rapid rise in XBB, but it doesn't look like it's particularly more severe than other variants," said Derek Smith, director of the Center for Pathogen Evolution at the University of Cambridge, told CBS News late last month.

"XBB, 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," explained Smith, who helps lead a National Institute of Health effort to analyze emerging variants.

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