(Reuters) — Doses of Moderna Inc’s COVID-19 vaccine are expected Sunday to be shipped on trucks and planes to healthcare facilities around the United States in a push to distribute the second approved COVID-19 vaccine.

The distribution of Moderna’s vaccine to more than 3,700 locations in the United States will vastly widen the rollout started last week by Pfizer Inc. The U.S. government plans to deliver 5.9 million Moderna shots and 2 million Pfizer shots this week.

The CDC Advisory Committee on Immunization Practices (ACIP) is expected to meet Sunday to discuss the allocation of initial supplies pf the second vaccine. NewsNation will stream the event in the embedded player at 10 a.m. CST.

But an ambitious target to get 20 million Americans started with their first shot of the two dose vaccine regimen before the end of the year could slip into the first week of January, U.S. Army General Gustave Perna told reporters on Saturday.

Moderna on Saturday moved vaccines from its manufacturing plants to warehouses operated by distributor McKesson Corp where they were packed into containers and loaded onto trucks. Shipments are departing Sunday and will start reaching healthcare providers as soon as Monday, Perna said.

The Food and Drug Administration on Friday issued an emergency use authorization for Moderna’s vaccine. The vaccine developed by Pfizer and its German partner BioNTech SE was authorized on Dec. 11.

Vials of Moderna’s vaccine were filled in pharmaceutical services provider Catalent Inc’s facility in Bloomington, Indiana. McKesson is shipping doses from facilities including Louisville, Kentucky and Memphis, Tennessee – close to air hubs for United Parcel Service Inc and FedEx Corp.

The start of delivery for the Moderna vaccine will significantly widen availability of COVID-19 vaccines as U.S. deaths caused by the respiratory disease reached more than 310,000 last week in the 11 months since the first documented U.S. cases.

Some states are choosing to use Moderna’s shots for harder-to-reach rural areas because they can be stored for 30 days in standard-temperature refrigerators. Pfizer’s must be shipped and stored at -94 F, and can be held for only 5 days at standard refrigerator temperatures.

Initial doses were given to health professionals. Programs by pharmacies Walgreens and CVS to distribute the Pfizer vaccine to long-term care facilities are expected to start on Monday.

The U.S. Centers for Disease Control and Prevention will decide Sunday on who it will recommend to be next in line to receive COVID-19 vaccines. The populations under closest consideration include essential workers, those over 65, and people with pre-existing conditions.