Public health experts are concerned for omicron’s new subvariant XBB with one study suggesting the strain is resistant to Covid-19 boosters from prior infections.NBC News’ Valerie Castro has more on whether the U.S. is looking at another surge as hospitals are already overwhelmed with RSV and flu cases.Dec. 30, 2022XBB now dominant Covid variant in U.S.02:41Now PlayingXBB variant sparks new Covid concerns03:02UP NEXTNew study finds link between POTS and long COVID02:17US airports to implement COVID rules for travelers from China00:43Mixed reactions among Beijing residents as China rolls back Covid policies"