Shipments of Moderna Inc.'s vaccine, the second coronavirus vaccine approved by the U.S. Food and Drug Administration (FDA) on Friday, are set to arrive in states on Monday.

Moncef Slaoui, head of the U.S. COVID-19 vaccine program, said it was most likely the first Moderna vaccine shot would be given on Monday morning.

The shipping started Sunday. Vials of Moderna's vaccine were filled in pharmaceutical services provider Catalent Inc.'s facility in Bloomington, Indiana. Distributor McKesson Corp. is shipping doses from facilities in places including Louisville, Kentucky, and Memphis, Tennessee – close to air hubs for United Parcel Service (UPS) and FedEx who are to distribute the doses from warehouses for deliveries to hospitals and other sites.

"We look forward to the vaccine. It's going to be slightly easier to distribute because it doesn't require as low (a) temperature as Pfizer," Slaoui said on CNN's "State of the Union."

According to Slaoui, nearly 8 million doses will be distributed Monday, about 5.9 million of the Moderna vaccine and 2 million of the Pfizer-BioNTech vaccine.

Both FedEx and UPS said the shipments were running smoothly and everything was going exactly as planned.

Who takes precedence to get inoculated?

U.S. frontline essential workers and people aged 75 and older should be next in line to receive the Moderna vaccine, the U.S. Centers for Disease Control and Prevention's (CDC) Advisory Committee on Immunization Practices recommended on Sunday.

By a vote of 13 to 1, the panel recommended people 75 and older, who number about 20 million, and certain frontline workers including first responders, teachers, food and agriculture, manufacturing, U.S. Postal Service, public transit, and grocery store workers, who total about 30 million, have the next priority for the vaccines.

About 200 million people including non-frontline workers such as those in media, finance, energy and IT and communication industries, people in the 65-74 age group, and those aged 16-64 years with high-risk conditions should be in the ensuing round, the panel recommended.

States, which are the ones distributing shots to their residents, will use the advisory panel's guidelines to decide how to allocate the vaccines while supplies are scarce.

Two COVID-19 vaccines approved

The FDA approval of the Moderna vaccine came about one week after the Pfizer-BioNTech COVID-19 vaccine got authorization on December 11.

Moderna on November 30 announced that the vaccine is 94.1 percent effective in preventing COVID-19, similar to that of the Pfizer-BioNTech vaccine, which during the previous large-stage trial proved to be 95 percent effective.

Both Moderna's and Pfizer-BioNTech's shots are so-called mRNA vaccines, which don't contain any coronavirus – meaning they cannot cause infection. Instead, they use a piece of genetic code that trains the immune system to recognize the spike protein on the surface of the virus, ready to attack if the real thing comes along.

Experts are hoping the two vaccines together will "break the back of the pandemic" when combined with masks and other precautions, said Dr. Arnold Monto of the University of Michigan, who chaired an advisory committee that publicly debated the shots' evidence ahead of the FDA's decisions.

In an attempt to shore up public support for vaccinations, Vice President Mike Pence and his wife Karen were injected with the Pfizer-BioNTech vaccine live on Friday.

Fewer doses than expected

However, states are complaining about receiving fewer doses than expected. At least a dozen states reported they would receive a smaller second shipment of the Pfizer vaccine than they had been told previously.

General Gustave Perna, chief operating officer of Operation Warp Speed, apologized on Saturday for "miscommunication" with states over the number of doses to be delivered in the early stages of distribution.

President-elect Joe Biden pledged earlier this month to have 100 million doses distributed in his first 100 days in office, and his surgeon general nominee said Sunday that it's still a realistic goal.

More than 17.8 million people have been diagnosed with coronavirus with over 317,000 deaths in the United States. The country has by far had the world's highest number of cases and deaths. 

(With input from Reuters, AP)