The federal government announced a $2.1 billion deal Friday with the French pharmaceutical company Sanofi and its British partner, GSK, to support the development of a coronavirus vaccine the companies are working on together.

The contract — the largest one yet from the U.S. government — includes the delivery of 100 million doses for the United States and is part of Operation Warp Speed, the Trump administration’s initiative to speed development of vaccines, treatments and diagnostics for the coronavirus.

The United States has now committed more than $8 billion to support the development of vaccines, or the pre-purchasing of doses, from Sanofi and GSK, Johnson & Johnson, Moderna, Novavax, Pfizer and AstraZeneca.

The first human testing of the experimental vaccine is expected to begin in September, with larger trials to test its effectiveness due to launch before year’s end. The companies anticipate having enough data to seek a regulatory decision in the first half of 2021 and plan to manufacture 1 billion doses per year.

“The global need for a vaccine to help prevent covid-19 is massive, and no single vaccine or company will be able to meet the global demand alone,” Thomas Triomphe, global head of Sanofi Pasteur, said in a statement.

The contract, which includes the option for the United States to buy an additional 500 million doses, includes support for clinical development of the vaccine and an advance purchase agreement. The U.S. government has committed billions of dollars to companies to lessen the financial risks of manufacturing vaccines before drugmakers know whether they work.

“The portfolio of vaccines being assembled for Operation Warp Speed increases the odds that we will have at least one safe, effective vaccine as soon as the end of this year,” Health and Human Services Secretary Alex Azar said in a statement.

The experimental vaccine from the two European companies includes a vaccine technology from Sanofi that was originally developed for influenza, combined with an adjuvant, or ingredient used to boost the immune response developed by GSK.

Most experts say that multiple vaccines will be necessary to meet global demand, and the United States has invested in a number of technologies. But the massive taxpayer investment has raised concerns about whether vaccines heavily subsidized by the government will be priced fairly. As rich countries scramble to reserve doses of vaccine, there is also worry they will monopolize products needed to make people safe around the world.

In addition to the U.S. deal, Sanofi and GSK reached an agreement earlier in the week to provide 60 million doses to the United Kingdom and are near a deal to provide 300 million doses to the European Union.On Friday, Pfizer announced that it would supply 120 million doses of its vaccine to Japan in the first half of 2021, pending regulatory approval.

Depending on the geography of the outbreak when vaccines become available, countries with fewer medical resources may need the vaccine more than rich countries.

Sanofi and GSK said in a statement that they have committed a “significant portion" of total supply in 2021 and 2022 to the Access to COVID‐19 Tools Accelerator, a global collaboration focused on providing equitable access to vaccines.

“Potential profits with our vaccine will be reinvested toward coronavirus-related research, long-term pandemic preparedness and increase in manufacturing capacity,” Sanofi spokesman Nicolas Kressmann said.

GSK has previously said that it does not plan to profit off its vaccine program during the pandemic.