After months of anticipation amid an unabating pandemic, the first delivery of Pfizer's COVID-19 vaccine will be delivered Monday to U.S. hospitals, according to officials.

The vaccine has been approved by the Food and Drug Administration for emergency use only. The vaccine is 95% effective.

On Saturday, boxes filled with the vaccine will be distributed from the Pfizer manufacturing location to various locations around the U.S. after they leave UPS and FexEx hubs. The vaccine shipments are going to 636 locations.

In a press briefing on Saturday, Gen. Gustave Perna, the chief operating officer of Operation Warp Speed, spoke about the delivery of Pfizer's vaccine.

“We expect 145 sites across all the states to receive the vaccine on Monday, another 425 sites on Tuesday, and the final 66 sites on Wednesday, which will complete the initial delivery of the Pfizer orders,” Perna stated.

Health departments will be giving out around 3 million doses over the coming week. Those who work in the front-lines of health care and those in care facilities will be receiving the vaccine first, Perna noted.

By the end of 2020, 20 million doses are expected to be administered to Americans.

The process of getting all Americans vaccinated could take several months.

The U.K. and Canada have also approved the vaccine and the U.K. started administering it last week. Two workers with the U.K. National Health Service experienced an anaphylactoid reaction after receiving the vaccine but had a history of severe allergies. Both made a full recovery.

Those under the age of 65 could experience side effects that include fevers, fatigue, headaches, chills, muscle aches and joint pain, FDA advisor Dr. Paul Offit told NPR.

"While today we applaud everybody who's been a part of the team, part of the collaboration, part of the success that brought us here today, we know that we are not done," Perna said. "We are not done until every American has access to the vaccine, until every American that wants it, receives it. This is our only goal. We work every day to achieve it."

German biotechnology company BioNTech and the US pharmaceutical giant Pfizer have produced one of the first Covid-19 vaccines
German biotechnology company BioNTech and the US pharmaceutical giant Pfizer have produced one of the first Covid-19 vaccines AFP / JOEL SAGET