Drug giant AstraZeneca has promised to deliver one billion doses of Oxford University's potential Covid-19 vaccine.
The pharmaceutical firm said it has secured the first agreements for at least 400 million doses of the vaccine.
It comes as earlier this week Health Secretary Matt Hancock said that if Oxford's Covid-19 vaccine candidate proves successful, then up to 30 million doses for the UK could be available by September.
AstraZeneca said it has now finalised its licence agreement with Oxford University for the “recombinant adenovirus vaccine”, which will be known as AZD1222.
But AstraZeneca has stressed that the vaccine may not work and that it is still waiting results from an early stage trial in southern England, before any moves towards late stage testing.
There are so far no approved treatments or vaccines for COVID-19 among those being tested by pharmaceutical giants across the world and experts predict a safe and effective means of preventing the disease could take 12 to 18 months to develop.
Other drugmakers including Pfizer, Johnson & Johnson and Sanofi are in various stages of vaccine development.
Pascal Soriot, chief executive of AstraZeneca, said: “This pandemic is a global tragedy and it is a challenge for all of humanity.
“We need to defeat the virus together or it will continue to inflict huge personal suffering and leave long-lasting economic and social scars in every country around the world. We are so proud to be collaborating with Oxford University to turn their ground-breaking work into a medicine that can be produced on a global scale."
He added: “We would like to thank the US and UK governments for their substantial support to accelerate the development and production of the vaccine. We will do everything in our power to make this vaccine quickly and widely available.”
The company has received more than $1 billion (£820 million) from the US Biomedical Advanced Research and Development Authority for the development, production and delivery of the vaccine.