An army of pilots, delivery drivers and pharmacists last month started to ship, distribute and administer millions of vaccine doses. The small vials are traveling on airplanes and trucks, and some times inside of specially made hand-held coolers. So far, two vaccines have been cleared by the Food and Drug Administration for emergency use in the U.S.: those by Pfizer-BioNtech and Moderna. Several other drugmakers also have agreements to provide their vaccines to the federal government once they are approved. AstraZeneca's vaccine, developed with Oxford University, was just approved for emergency use in the U.K. but is still in clinical trials in the U.S.