"The first vaccine will be administered in less than 24 hours," said Trump in a video released on his Twitter page.

"Our nation has achieved a medical miracle. We have delivered a safe and effective vaccine in just nine months. This is one of the greatest scientific accomplishments in history. It will save millions of lives and soon end the pandemic once and for all," added Trump.

The FDA granted an emergency use authorization for the vaccine, developed with German partner BioNTech, which was shown to be 95% effective in preventing the disease in a late-stage trial.

The FDA said the vaccine can be given to people aged 16 and older. Healthcare workers and elderly people in long-term care facilities are expected to be the main recipients of a first round of 2.9 million doses.

The U.S. government has said it will begin distributing the vaccine around the country immediately after FDA authorization, and that the first inoculations would happen early next week.

Millions of Americans could begin getting vaccinated this month, especially if a second vaccine from Moderna Inc MRNA.O is quickly approved.

The Pfizer/BioNTech vaccine was first approved in Britain earlier this month, and UK residents began receiving the shots on Tuesday (December 8). Canada also authorized the vaccine and expects to start inoculations next week.