The US government will pump up to $1.2bn (£980m) into the development of AstraZeneca and the University of Oxford’s coronavirus vaccine, it has announced.
The US will also order 300 million doses of the vaccine once production begins, it said.
The news comes after AstraZeneca said it had the capability to produce one billion doses of the vaccine this year, and that it would begin supplying 100 million doses to the UK government in September, provided clinical trials prove successful.
In a statement, the company acknowledged that the vaccine might not work, but said it was ready to facilitate trials in several countries if early UK trials showed positive results.
It also said it would work with the World Health Organisation to ensure the vaccine was distributed fairly around the globe.