Five percent of all produced COVID-19 vaccine will be held back for emergencies and states will have the option of trading vials within the government’s ordering system to get the kind they want.

Those are just a few of the details we’re learning about how the vaccine will move around the nation as distribution comes closer, potentially as early as Friday or Saturday.

Paul Ostrowski, who leads supply, production and distribution for the federal government’s Operation Warp Speed, walked USA TODAY through the process.

Here’s what else we know: Operation Warp Speed, the White House COVID-19 initiative, plans to only ship half of all vaccine available each week. The other half will be held in storage and be released just before the second dose is due for those vaccinated the first time.

Two vaccines are in the final phases of the Food and Drug Administration emergency authorization process, with Pfizer and its partner BioNTech’s coming before the agency this week, followed by Moderna next week.

How will vaccine be shipped?
The vaccine is shipped in glass vials, five-dose vials for Pfizer and 10-dose vials for Moderna. The Pfizer vaccine must be stored at minus 94 degrees or below; Moderna’s at minus 4 degrees.

Because of the ultracold storage requirements of the Pfizer vaccine, it is being stored either at Pfizer production facilities or what are known as “freezer farms,” storage sites filled with row upon row of ultracold freezers about the size of a large home refrigerator, said Ostrowski.

Pfizer will ship its vaccine using UPS and FedEx as its main distributors. Moderna’s vaccine distribution is being coordinated by McKesson, the nation’s largest medical supply distributor.