Moderna's (NASDAQ:MRNA) lucrative relationship with the U.S. government took another big step forward on Sunday. The Biomedical Advanced Research and Development Authority (BARDA) amended its contract with the clinical-stage biotechnology company for an additional commitment of up to $472 million.

In April, BARDA agreed to a commitment of up to $483 million to support the advancement of Moderna's coronavirus vaccine candidate, mRNA-1273, from phase 1 trials through FDA licensure. The total value of the award was boosted to $955 million to support a 30,000 person phase 3 trial, which is a lot more participants than originally intended.

Doctor checking in samples of blood.

Image source: Getty Images.

Tomorrow, July 27, volunteers in the phase 3 COVE study will randomly begin receiving either two shots of mRNA-1273 spaced 29 days apart, or a placebo. Investigators will mainly be measuring first occurrences of COVID-19, with two long years of observations beginning 14 days after participants receive their second dose.

In addition to running a giant phase 3 trial, Moderna is also manufacturing huge quantities of mRNA-1273 at risk. With help from a collaboration with Lonza (OTC:LZAG.Y), the company is on track to begin delivering between 500 million and 1 billion doses annually in 2021.

Moderna's vaccine candidate will be one of the first to begin a phase 3 trial in the U.S., nearly one month after Oxford University began testing AZD1222 in a 5,000-volunteer study in partnership with AstraZeneca (NYSE:AZN). While we've seen results from dozens of patients treated with mRNA-1273, AstraZeneca and Oxford recently published results from a phase 1 trial with 1,077 randomized to receive AZD1222 or a placebo.