The Trump administration has committed to spend $1.95 billion on 100 million doses of a potential COVID-19 vaccine being developed by Germany’s BioNTech and US pharma giant Pfizer, which will be distributed free of charge to American citizens.

BioNTech announced on Wednesday that the supply agreement signed by the White House also includes the option for the US government to purchase a further 500 million doses, subject to the vaccine being granted regulatory approval.

Several governments have signed agreements with some of the 24 groups currently testing a coronavirus vaccine on humans, including a promising candidate developed by Oxford university and AstraZeneca, but most other purchasers have refused to reveal the price paid per dose.