The US public will start receiving the Pfizer/BioNTech coronavirus vaccine from Monday after it was authorised for emergency use, officials say.
The first three million doses of the vaccine would be shipped "across all states" this weekend, said General Gustave Perna, who is overseeing distribution.
The vaccine offers up to 95 percent protection against Covid-19 and was deemed safe by the Food and Drug Administration (FDA).
The FDA said its approval for use was a "significant milestone" in the crisis.
The US agency authorised the emergency use of the Pfizer/BioNTech vaccine on Friday, after coming under intense pressure from the Trump administration to do so.
A mass inoculation drive using doses of the same vaccine is already underway in the UK.
During a news conference today, General Perna - speaking for the US government's vaccination campaign Operation Warp Speed - said doses of the vaccine would be packed into shipping containers for transportation "within the next 24 hours".
"Expect 145 sites across the states to receive the vaccine on Monday, another 425 sites on Tuesday, and the final 66 sites on Wednesday," he said, adding that next week's distribution would complete the initial delivery of the Pfizer/BioNTech vaccine and cover about three million people.
General Perna told reporters he was "100 percent confident" that the doses "needed to defeat the enemy Covid" would be transported safely.
He warned, however, that while it had been a week of progress, "we are not done until every American has access to a vaccine".
The Pfizer vaccine has already received regulatory approval in the UK, Canada, Bahrain and Saudi Arabia. Like those countries, US health authorities are expected to prioritise health workers and care home residents for the first doses.
More Americans outside the highest-priority groups are likely to be able to get the vaccine in January, with general availability expected by April.
Coronavirus deaths have been rising sharply since November in the US. On Wednesday, the country recorded more than 3000 deaths - the highest total in a single day anywhere in the world.