Pfizer's COVID-19 vaccine is expected to begin rolling out across hundreds of sites in the country on Sunday (Dec. 13), Army Gen. Gus Perna announced on Saturday.

HuffPost reports that the doses are currently being packaged at Pfizer's facility in Michigan, to be delivered to 145 predesignated sites across 50 states for Monday. This will be followed by further shipments to 425 different sites on Tuesday, and an additional 66 sites on Wednesday. In total, there are around 2.9 million doses to arrive across the sites. However, it's to be expected that each site will receive a different amount accounting for the at-risk population in each area.

"Expect 145 sites across the states to receive the vaccine on Monday, another 425 sites on Tuesday, and the final 66 sites on Wednesday," Perna said in a press conference on Saturday morning. Perna explained that the vaccine distribution will be assisted thanks to "a great collaboration between UPS and FedEx," and has ensured the public that the doses will be transported using the required freezers. "We want to ensure perfection in the vaccine. We don't want anything going into an arm that would be a problem," he added.

The news comes as the U.S Food and Drug Administration granted an emergency use authorization for the vaccine this week. The vaccine, which is said to be up to 95 percent effective in protecting individuals from COVID-19, was granted safe for public use and Perna has indicated that more Americans could receive it as early as three weeks from now. A second coronavirus vaccine, produced by Moderna, is scheduled to go through FDA approval this coming week.