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What you need to know about the 'alarming' new XBB.1.5 COVID subvariant

A new COVID-19 Omicron subvariant is causing concern among scientists monitoring the virus's spread and evolution, CNN reports. On Friday, the Centers for Disease Control and Prevention's COVID-19 variant dashboard revealed startling data concerning a variant with features that could encourage a surge of COVID cases in the U.S. — XBB.1.5.

Throughout December, the CDC estimates that XBB.1.5 has more than doubled its share of positive COVID cases every week, leading it to rise from 4 percent to 41 percent of new infections by the end of the month. XBB.1.5 is responsible for 75 percent of new cases in the Northeast, per the CDC. Virologists and epidemiologists predict that the features of this Omicron variant could drive a surge of positive cases in the U.S. However, according to CNN, it remains to be seen how extensive or severe that wave could be. 

Despite lingering concerns that China's ongoing surge following the unraveling of its zero COVID policy would pose a threat, experts say XBB.1.5 emerged in the U.S. According to GISAID, a global initiative to catalog and track variants of COVID, the subvariant was first detected in New York and Connecticut in late October. It's the product of two descendants of BA.2, the subvariant that drove a small surge in the U.S. in April. 

A recent study found that the XBB sublineage had higher levels of immune evasion, making it exponentially less likely to be neutralized by antibodies in previously infected or vaccinated people. Scientists behind the study called the level of immune evasion  "alarming," suggesting that it could be detrimental to the efficacy of COVID vaccines. 

XBB.1.5 also has a genetic mutation that allows it to bind more tightly to ACE2, the entryway for viruses into human cells, meaning it is more infectious. 

"The mutation is clearly letting XBB.1.5 spread better," Jesse Bloom, a computational virologist at the Fred Hutchinson Cancer Center who flagged the mutation, wrote in an email to CNN.