The pop icon has postponed two of her upcoming shows a week after launching her most recent Las Vegas residency. "After welcoming all of you to the new year from the stage in Las Vegas, I've been welcomed with a new year flu," Christina, 43, wrote on her Instagram Stories. "I am sorry to share that my two shows this weekend will be rescheduled while I rest - and I cannot wait to be back on that stage in a few weeks,"