The US Food and Drug Administration has found the Moderna coronavirus vaccine is safe and 94 per cent effective, clearing the way for emergency approval.

It comes a day after Americans began receiving Pfizer’s vaccine, with supplies reaching 141 of 145 locations targeted by the US government.

On Wednesday morning (Australian time), FDA scientists gave a full endorsement of Moderna’s vaccine.

In a 54-page document, the experts wrote there were “no specific safety concerns” and it was rare for the vaccine to induce a severe adverse reaction.

The FDA affirmed Moderna’s finding that its vaccine had 94.1 per cent efficacy based on Moderna’s phase three analysis, which involved 30,000 people in the US.

Side effects of the drug included fever, headaches, and muscle and joint pain.

The FDA vaccine panel will meet at the end of the week to discuss granting an emergency use authorisation.

If approved, the Moderna vaccine, which requires two doses, will become only the second coronavirus vaccine given emergency clearance.

The FDA released similar data about Pfizer and German partner BioNTech’s vaccine last week before granting emergency use authorisation. The first shipments were sent out on Sunday.

Nurse Sandra LIndsay became patient zero in the US coronavirus vaccine program. Photo: AAP

The US government is aiming to distribute the first wave of 2.9 million vaccine doses to 636 locations nationwide by the end of the week.

But severe storms expected in some parts of the country this week could pose challenges to vaccine shipments.

Facilities in four island territories – American Samoa, the US Virgin Islands, the North Mariana Islands and Guam – are still waiting supplies, the US Department of Health and Human Services said on Tuesday (Australian time).

HHS Secretary Alex Azar said the US Centres for Disease Control and Prevention provided $US145 million ($A192 million) to states to help with distribution.

“Literally millions of doses right now are getting out there to the American people. And by next week, we believe we could be having a second vaccine,” Mr Azar said  at George Washington University Hospital as part of a vaccination kick-off event.

“By the end of February, what you saw today could be replicated a 100 million times, a 100 million shots in arms between the first and booster vaccine.”

Federal officials are in talks with Pfizer to acquire additional doses beyond the 100 million already purchased.

Meanwhile, AstraZeneca has enrolled 22,000 people in US clinical trials and could submit for emergency authorisation as soon as February.