The United States government has agreed to pay $1.95 billion to both Pfizer and BioNTech for the delivery of 100 million doses of their new coronavirus vaccine. Both companies announced on Wednesday that the deal will only push through if their vaccine is proven to be safe and effective against the deadly infection.

The proposed deal is the largest of its kind between a government and private companies involving a potential treatment for the coronavirus. According to the U.S. Department of Health and Human Services (HHS), the deal does include a clause for an additional 500 million doses if the vaccine is proven to be effective.

New York-based Pfizer and German biotech firm BioNTech are jointly developing four different types of vaccine candidates for the coronavirus. The U.S. is open to purchasing any of the four vaccine candidates that are to proven to be the safest and most effective against the virus. The particular vaccine has to also pass all regulatory requirements and be approved for public use.

The newly signed agreement is part of the Trump administration's Operation Warp Speed initiative, which is aimed at accelerating the development and distribution of vaccines to all Americans. HSS Secretary Alex Azar had said that the country is betting on a number of potentially effective vaccines produced by multiple companies to increase its chances of finding at least one that is effective and safe to use before the year ends.

Both companies are now preparing to launch a larger trial of their vaccines, which will involve up to 30,000 participants. The companies expect to launch the trial next month once they receive regulatory approval.

Among the four vaccines that are being developed by the companies, the most promising candidate is their BNT162b1 vaccine. According to data from their early-stage clinical trials, the vaccine had proven to be effective in producing neutralizing antibodies, which is necessary for building immunity to the coronavirus.  

Following the news of the proposed deal, Pfizer's share prices surged by 3.8 percent, while BioNTech's stock price went up 4 percent.

If the deal goes through, HHS will be the leading agency tasked with delivering the vaccines to different parts of the country under the government's direction. HHS stated that the vaccines will be made available to all infected Americans "at no cost." However, it still remains unclear how the HHS will determine which states will get the much-needed doses first.