The United States has green-lighted the Pfizer-BioNTech Covid-19 vaccine, paving the way for its imminent rollout across the country, with President Donald Trump promising the first immunisations would take place “in less than 24 hours.”

“I am authorising the emergency use of Pfizer-BioNTech Covid-19 Vaccine for the prevention of Covid-19,” Denise Hinton, the Food and Drug Administration's chief scientist wrote in a letter to a Pfizer executive.

President Donald Trump immediately released a video on Twitter, where he hailed the development.

“The first vaccine will be administered in less than 24 hours,” Trump said in a televised address released on Twitter.