National numbers, January 15

Last week, I wrote that a combination of holiday travel/gatherings and the latest Omicron subvariant, XBB.1.5, was driving a winter surge. This week, COVID-19 metrics suggest that the surge may have peaked, though we’ll need more data to say for sure—and XBB.1.5 remains a concern.

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XBB.1.5 FAQ: What you should know about the latest Omicron subvariant

XBB.1.5 is the latest Omicron subvariant to spread rapidly through the U.S. It is, of course, more transmissible and more capable of evading immunity from past infections than other versions of Omicron that have gone before it, as this lineage continues mutating. Scientists are still learning about XBB.1.5; it emerged from the U.S. during the holiday season, which has posed surveillance challenges. But we know enough to say that this variant is bad news for an already overstretched healthcare system.

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National numbers, January 8

Well, here we are: the winter COVID-19 surge. It may have happened later than some experts predicted, but the U.S. is clearly now experiencing an uptick in virus transmission as the latest, most contagious Omicron subvariants collide with holiday travel and gatherings.

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