A new, fast-spreading variant of COVID-19 is sweeping across the nation, making it the most widely circulating iteration of the virus in the U.S. and around the world, according to the Centers for Disease Control and Prevention. The mutation, called JN.1, is a subvariant of Omicron that was first detected by the World Health Organization in late August. At the time it appeared to be spreading slowly but as temperatures have dipped, JN.1 has spiked. In mid-October, CDC data shows JN.1 made up about 0.1% of all COVID-19 cases around the country. As of Jan. 20, the CDC estimates that's...