The new omicron subvariant, known as XBB.1.5, is spreading like wildfire across the U.S. As colder weather brings in peak COVID infections, this novel mutation is beginning to worry health professionals. So, what are some of the unique features of the strain that is now gripping swaths of the country? THE NEW OMICRON SUBVARIANT XBB.1.5: WHAT YOU MUST KNOW NOW First, this subvariant is immuno-evasive. It’s not as susceptible to natural immunity or vaccines — and it is very contagious, health professionals say.  In a phone interview with Fox News Digital, Fox News medical contributor Dr. Marc Siegel explained that there are actually two subvariants at play: XBB and XBB.1.5.…