U.S. Air Force A1C Tyler Lancaster, 60th Healthcare Operations Squadron, medical technician, administers an initial COVID-19 vaccine to Col. Corey Simmons, 60th Air Mobility Wing commander, Dec. 29, 2020 at Travis Air Force Base, California. The vaccine requires two doses per person, separated by about four weeks between doses. It is designed to protect against the coronavirus, and officials are encouraging all prioritized personnel to take the vaccine as it becomes available. (U.S. Air Force photo by Airman 1st Class Alexander Merchak)