Washington: The US has green-signalled the Pfizer-BioNTech Covid-19 vaccine on Friday, paving the way for millions of vulnerable people to receive their shots in the world's hardest-hit country.
US President Donald Trump had released a video on Twitter where he hailed the news as a "medical miracle" and said the first immunizations would take place "in less than 24 hours".
It comes as infections in America soar as never before, with the grim milestone of 300,000 confirmed deaths fast approaching.
The US is the sixth country to approve the two-dose regimen after Britain, Bahrain, Canada, Saudi Arabia and Mexico.
The move has come earlier than expected and capped a day of drama after it was widely reported that the White House had threatened to fire Food and Drug Administration chief Stephen Hahn if he did not grant emergency approval on Friday.
Trump's intervention reinserts politics into the scientific process, which some experts have said could undermine vaccine confidence.
The US is seeking to inoculate 20 million people this month alone, with long-term care facility residents and health care workers at the front of the line. The government also said on Friday that it is buying 100 million more doses of the Moderna vaccine candidate, amid reports the government passed on the opportunity to secure more supply of the Pfizer jab.
The purchase brings its total supply of Moderna doses to 200 million, enough to immunize 100 million people with the two-shot regimen that could be approved as early as next week. Both frontrunners are based on mRNA (messenger ribonucleic acid), a major victory for a technology that had never previously been proven.
Two other vaccine candidates stumbled on Friday: France's Sanofi and Britain's GSK said their vaccine would not be ready until the end of 2021.
In Australia, the development of a vaccine at The University of Queensland was abandoned on Friday after clinical trials produced a false positive HIV result among subjects involved in early testing.