MIAMI (AP) — The COVID-19 vaccination campaign at Miami’s largest hospital starts with the delivery of frozen glass vials that arrive with armed guards. The vials are immediately whisked to a secret location, where they are placed inside a padlocked freezer. The Associated Press was given exclusive access to a recent day of vaccinations at Jackson Memorial hospital system. The effort is an anxious undertaking for both vaccine providers and Americans seeking the shots, and everyone has to watch the clock. The hospital staff can thaw out only as much COVID-19 vaccine as the hospital can administer that same day. Once mixed, the vaccine is good for only six hours.