Biden urged Americans to remain “vigilant” over the holidays, adding that Pfizer’s and Moderna’s vaccines likely won’t stop the deaths of “tens of thousands” people from Covid. “Taking the vaccine from a vial into the arm of millions of Americans is one of the biggest operational challenges the United States has ever faced,” he said. “In the meantime, the pandemic rages on. Experts think it could get worse before it gets better,” he added.