The biggest logistical effort in the history of the United States is underway and beginning Monday it will lead to the country's biggest vaccination campaign as Pfizer's COVID-19 vaccine takes on the virus that has killed more than 300,000.

Vaccinations will begin Monday, Dr Nancy Messonnier, director of the National Center for Immunization and Respiratory Diseases at the Centers for Disease Control and Prevention (CDC), said during a meeting Saturday.

With a second vaccine from Moderna expected to follow shortly, as many as 40 million doses could be delivered by the end of the year — enough to vaccinate the CDC's first priority groups — healthcare workers at high risk of exposure to the virus and residents of nursing homes and other long-term-care facilities.

As hospitals prepared to receive the vaccine, the US on Saturday reported its 16 millionth coronavirus case, according to federal officials.

The country reported its highest daily cases, more than 232,700, on Friday, according to a Reuters tally. In the latest seven-day average, the United States is reporting 2,411 deaths per day, the highest seven-day average since the pandemic started.

US hospitalizations for COVID-19 were 107,684 by the end of Friday, the highest so far.

General Gustave Perna, the chief operating officer of Operation Warp Speed, the federal effort to bring a vaccine to market, said Saturday at a news conference that nearly 3 million doses of the vaccine, manufactured by Pfizer and BioNTech, are being sent by plane and guarded truck to 145 sites on Monday, 425 on Tuesday and 66 on Wednesday.

Early Sunday morning, boxes packed at Pfizer's plant in Kalamazoo, Michigan, were being shipped to UPS and FedEx distribution hubs, where they were to be sent to the 636 locations across the country. No vaccine doses were positioned in advance of the Food and Drug Administration approving the vaccine on Friday night, officials said.

Both UPS and FedEx have said that doses will arrive at their destinations a day after leaving the Pfizer facilities. Pfizer's plant in Michigan will attach special Bluetooth- and radio-enabled tracking tags to each shipment.

"This is a historic day," said Richard W. Smith, who oversees operations in the Americas for FedEx Express.

Both companies said the shipments would be closely tracked and monitored and would be given priority over other packages.

To ship its vaccine, Pfizer designed specialized containers packed with enough dry ice to keep a minimum of 975 doses cool for up to 10 days. Each comes with a tracking device.

UPS and FedEx will split distribution of the vaccine throughout the country. After the initial shipments arrive, all Pfizer dosing sites will receive another shipment from UPS of 40 pounds of extra dry ice to keep the vaccines at a subzero temperature, officials said.

FDA officials on Saturday said vaccination sites will have medical personnel on hand to deal with side effects such as severe allergic reactions.

The officials made the comments after two people in the UK experienced reactions after getting the vaccine. That prompted the country's health authorities to warn that people with a history of severe allergic reactions to vaccines shouldn't get the COVID-19 shot. Both people already had serious allergic histories.

The vaccine from Pfizer was authorized in England a week ago.

New York Governor Andrew Cuomo, who with several other governors vowed to review the vaccine before allowing it in their states, announced late Friday that state officials have approved the drug.

"The vaccine, that is the weapon that ends the war," Cuomo said in a press briefing Saturday.

Agencies contributed to this story.