Pfizer (NYSE:PFE) and BioNtech (NASDAQ:BNTX) are jointly developing four mRNA-based vaccine candidates for the SARS-CoV-2 coronavirus. And on Wednesday morning, the companies announced that they had signed a deal with the U.S. government's Health and Human Services (HHS) and Defense departments to supply them with at least 100 million doses of whichever candidate earns regulatory approval or emergency use authorization -- assuming one does.

Washington will pay the partners $1.95 billion upon delivery of those 100 million doses. The agreement also gives the government the option to purchase 500 million additional doses. Note that on Monday, the two companies announced a similar (albeit smaller) deal with the U.K. government. 

Pfizer and BioNtech are currently running a phase 1/2 clinical trial for the coronavirus vaccine candidates in the BNT162 program, and they recently released positive study data for BNT162b1 -- the most advanced of the bunch. Further, the healthcare companies plan to start a phase 2b/3 clinical trial by the end of July, pending regulatory approval. That study is expected to enroll up to 30,000 healthy participants, and will test the safety and efficacy of the chosen vaccine candidate. It is also worth noting that the Food and Drug Administration has granted fast-track designation to two of the candidates in the program, BNT162b1 and BNT162b2.

Doctor holding a vial with a sign saying "COVID-19 Vaccine Coronavirus."

Image source: Getty Images.

Pfizer and BioNtech aren't the only ones attempting to develop mRNA-based COVID-19 vaccines -- Moderna (NASDAQ:MRNA) is too, and it's also well advanced in the development process. That biotech company plans to start a phase 3 clinical trial on July 27 for its lead candidate, mRNA-1273. The pivotal study will enroll about 30,000 participants, and its primary endpoint will be "the prevention of symptomatic COVID-19 disease." As the worldwide efforts to find a vaccine heat up, the next few months will be critical for Pfizer and BioNtech.