The Sanofi-GSK deal is for 100 million doses - at two per person - and gives the U.S. government an option to purchase an additional 500 million doses. 

The two companies' inoculation is combination of a vaccine based on Sanofi's flu shots and a complementary technology from GSK called an adjuvant, designed to improve the vaccine's potency.

The deal comes after GSK and Sanofi signed an agreement with the UK government for 60 million doses of coronavirus vaccine.

The purchase falls under the Trump administration's so-called 'Operation Warp Speed', intended to bring a Covid-19 vaccine to the market by the end of 2020.

The deal with the U.S government cost works out at round £32 per person inoculated.

That is almost identical to the £30 per patient the U.S. agreed to pay Pfizer Inc and BioNTech SE when it inked a nearly £1.5 billion deal for 50 million courses of that potential vaccine last week.

The global need for a vaccine to help prevent COVID-19 is massive, and no rush a single vaccine or company will be able to meet the global demand alone,” said Thomas Triomphe, head of Sanofi’s vaccine division.

Health and Human Services  Secretary Alex Azar said the range of vaccines being increases the odds that “we will have at least one safe, effective vaccine as soon as the end of this year”.

“Today’s investment supports the Sanofi and GSK adjuvanted product all the way through clinical trials and manufacturing, with the potential to bring hundreds of millions of safe and effective doses to the American people.”

The agreement marks the second contract for the Franco-British pair's vaccine candidate after they agreed earlier this week to supply 60 million doses to the British government.