The Trump administration has agreed to pay vaccine maker Novavax $1.6 billion to develop, test and produce 100 million doses of a coronavirus vaccine around the start of 2021, the company announced on Tuesday.

It amounts to a big bet on the Maryland-based biotech company, which has never brought a product to market.

It’s the largest deal yet for Operation Warp Speed — which the New York Times describes as “the sprawling federal effort to make coronavirus vaccines and treatments available to the American public as quickly as possible.”

The Novavax vaccine is aimed at boosting the body’s natural immune response with microscopic particles carrying tiny fragments of the Covid-19 virus.

Even Novavax president and CEO Stanley Erck admits the gamble might not pay off.

“Nobody knows for sure,” Erck said Tuesday morning on CNBC. Whether the vaccine works or not must be determined through clinical trials, he added.

Phase 1 of the trials will be completed in about a week in Australia, Erck told Reuters, with a second round of trials beginning in August or September and Phase 3 testing starting in October.

The Warp Speed award pays for testing of the Novavax vaccine and production of 100 million doses, to be delivered starting in the fourth quarter of 2020 and completed “by January or February of next year,” Erck said. The 100 million doses are enough for 50 million people to receive an initial injection and a booster.

In a statement, Health and Human Services Secretary Alex Azar said that Novavax adds to Operation Warp Speed’s “diverse portfolio of vaccines increases the odds that we will have a safe, effective vaccine as soon as the end of this year.”

Another company, Sanofi, has received more than $30 million in federal funding to develop a similar vaccine that stimulates the body’s own immune system to fight the virus.

Other pharmaceutical companies, including Johnson & Johnson, Moderna and AstraZeneca, are working on different types of vaccines.