Department of Defense personnel line up to receive the initial dose of the COVID-19 vaccine at the Physical Fitness Center, Travis Air Force Base, California, Jan. 8, 2021. The vaccine requires two doses per person, separated by about four weeks between doses. It is designed to protect personnel against the coronavirus, and officials are encouraging all prioritized personnel to take the vaccine as it becomes available. (U.S. Air Force photo by Heide Couch)