WASHINGTON (AP) — Pfizer and BioNTech will supply the U.S. with an additional 100 million doses of their COVID-19 vaccine under a second agreement.

The drugmakers said Wednesday that they expect to deliver all the doses by July 31.

Pfizer already has a contract to supply the government with 100 million doses of its vaccine, which requires two doses per patient.

Under the nearly $2 billion deal announced Wednesday, the companies will deliver at least 70 million of the additional doses by June 30, with the remaining 30 million doses to be delivered no later than July 31. The government also has the option to acquire up to an additional 400 million doses.

Health and Human Services Secretary Alex Azar said in a statement that the latest deal can give people confidence "that we will have enough supply to vaccinate every American who wants it by June 2021."

Pfizer's vaccine was the first to gain authorization for emergency use from the Food and Drug Administration and initial shipments went to states last week. It has now been joined by a vaccine from Moderna, which was developed in closer cooperation with scientists from the National Institutes of Health.

Moderna's vaccine, which also requires two doses, comes under the umbrella of the government's own effort, which is called Operation Warp Speed. That public-private endeavor was designed to have millions of vaccine doses ready and available to ship once a shot received FDA approval.

A law dating back to the Korean War gives the government authority to direct private companies to produce critical goods in times of national emergency. Called the Defense Production Act, it's expected to be invoked to help Pfizer secure some raw materials needed for its vaccine.

Pfizer already had a contract to supply the government with 100 million doses of its vaccine under Operation Warp Speed, but government officials have said it's more of an arms-length relationship with the company and they don't have as much visibility into its operations.

The drugmaker will receive nearly $2 billion for that deal as well.

Azar said last week that the government was negotiating with Pfizer for more doses, but details provided Tuesday about the company's desire for better access to supplies are new.

"With these 100 million additional doses, the United States will be able to protect more individuals and hopefully end this devastating pandemic more quickly," said Pfizer CEO Albert Bourla. "We look forward to continuing our work with the U.S. government and healthcare providers around the country."

The vaccine from Pfizer and German pharmaceutical BioNTech immediately raised hopes of taming a pandemic that has killed nearly 320,000 people in the U.S. and hobbled much of the national economy. Health care workers and nursing home residents topped the list as local TV stations across the country began broadcasting scenes of the first vaccinations. Some polls show skepticism about getting vaccinated may be easing.

After early failures with testing, Trump administration officials are hoping to write a very different ending with vaccines. Operation Warp Speed has financed the development, manufacture and distribution of millions of doses, with the goal of providing a free vaccine to any American who wants one.

Operation Warp Speed is on track to have about 40 million doses of vaccine by the end of this month, of which about 20 million would be allocated for first vaccinations. Distribution of those doses would span into the first week of January. Both the Pfizer and Moderna vaccines require two shots to be fully effective.

The New York Times first reported the new details of negotiations between Pfizer and the Trump administration.