Distribution of the second COVID-19 vaccine authorized in the US started on Sunday as initial shipments left a factory in the Memphis area.
The jabs are expected to be administered from Monday, just three days after the Food and Drug Administration authorised their emergency rollout. The FDA had first approved Pfizer Inc and BioNTech SE's COVID-19 vaccine earlier this month.
McKesson CEO Brian Tyler told NBC News in a statement on Sunday that the company is "honored to be a partner with the USA government and other private-sector companies such as Moderna to support in the distribution of COVID-19 vaccines and the ancillary supply kits".
Nationwide, more than 219,000 people per day on average test positive for the virus, which has killed more than 314,000 in the United States and almost 1.7 million worldwide.
UPS and FedEx trucks stocked with the vaccine were reportedly seen leaving McKesson's distribution centers in MS and Kentucky early Sunday afternoon.
The CDC outlined that all people who receive the vaccine be physically monitored at the site. The FDA announced the authorisation the day after the agency's advisory panel of outside experts endorsed its use.
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But no matter what the CDC says, there will be differences from state to state, because their health departments have different ideas about who should be closer to the front of the line. Apart from this total first round of 6.4 million doses, an extra 500,000 doses are being kept for any emergency. Both vaccines appear safe and strongly protective in large, still unfinished studies.
Trade Minister Mohamed Azmin Ali said the government is also in talks with other pharmaceutical companies to secure more vaccines.
The Trump administration's Operation Warp Speed program has invested billions into the manufacturing of Moderna's vaccine as well as its distribution.
Elsewhere, Donald Trump's surgeon general was defending the president not receiving a coronavirus vaccine, saying there were medical reasons for it.
The agency issued new guidelines, outlining that people with a history of severe allergic reactions to things not related to vaccines - such as food, animals, environmental or latex - may still get vaccinated.