The U.S. will administer its first doses of Pfizer’s recently approved coronavirus vaccine on Monday, Dec. 14, as part of a historic mass vaccination effort, while related deaths tick toward the 300,000 mark.

The first of almost 3 million shots will go to health care workers and residents of nursing homes, prioritized as the most vulnerable. Federal officials estimate that residents of long-term care facilities account for 40% of virus deaths to date.

Workers at a Pfizer plant in Portage, Mich., loaded the first doses onto trucks on Sunday, and UPS and FedEx routed the precious, sub-freezing product across the country. The vaccines were taken from Pfizer’s Portage facility to Gerald R. Ford International Airport in Grand Rapids. Trucks departing the Michigan facility were met with cheers Sunday.

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Boxes containing the Pfizer-BioNTech COVID-19 vaccine are prepared to be shipped at the Pfizer Global Supply Kalamazoo manufacturing plant in Portage, Mich., Sunday, Dec. 13, 2020. (AP Photo/Morry Gash, Pool)

Boxes containing the Pfizer-BioNTech COVID-19 vaccine are prepared to be shipped at the Pfizer Global Supply Kalamazoo manufacturing plant in Portage, Mich., Sunday, Dec. 13, 2020. (AP Photo/Morry Gash, Pool)

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FedEx took to Twitter on Monday to announce the successful completion of initial deliveries.

“We’ve safely made our first deliveries of @pfizer- @BioNTech_Group COVID-19 vaccines,” FedEx wrote in a Tweet. “We’re honored to be able to use our network to transport these critical vaccines in the U.S., and eventually the world.”

FedEx had also tweeted that planes touched down in Memphis yesterday after vaccines made a reported safe departure out of Grand Rapids to their final destinations. Quick transport is key for the vaccine, especially since this one must be stored at extremely low temperatures — about 94 degrees below zero.

FedEx workers transport vaccine doses in Grand Rapids, Mich. (FedEx)

FedEx workers transport vaccine doses in Grand Rapids, Mich. (FedEx)

UPS also reflected on the historic day in a Tweet on Sunday, writing: "It was a whirlwind of a day that was months in the making. To our partners in the healthcare, logistics and government sectors, and to the @UPSers who made today's #vaccine logistics possible...thank you!"

FIRST SHIPMENT OF PFIZER-BIONTECH CORONAVIRUS VACCINE LEAVES MICHIGAN FACILITY

The first shipments were said to arrive in 145 distribution centers Monday across 50 states, with an additional 425 sites getting shipments Tuesday and the remaining 66 on Wednesday. The vaccine, co-developed by German partner BioNTech, is being doled out based on each state's adult population.

Despite initial doses now delivered nationwide, the vaccine still faces significant distrust and skepticism among a large proportion of Americans.

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A survey from The Associated Press-NORC Center for Public Affairs Research found that about half of Americans want to get the vaccine as soon as possible. Another quarter aren’t sure, while the remaining quarter say they aren’t interested. Some simply oppose vaccines in general. Others are concerned that the vaccines have been rushed and want to see how the rollout goes.

Dr. Stephen Hahn, the commissioner of the FDA, which approved the Pfizer vaccine Friday, has repeatedly insisted that the agency’s decision was based on science, not politics. 

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Fox News' Evie Fordham and The Associated Press contributed to this report.