A leader in the race to develop a vaccine that could bring the ongoing COVID-19 pandemic to a close has taken another important step forward. AstraZeneca (AZN 2.65%) has begun a late-stage clinical trial in the U.S. with its coronavirus vaccine candidate, AZD1222, the company announced Monday.

Developed in partnership with Oxford University, AZD1222 employs the husk of an inactivated virus to deliver genetic material. Injections with the viral vector-based vaccine candidate appear to train human immune systems to recognize SARS-CoV-2 and shut it down before it leads to COVID-19. 

Healthcare worker administering a vaccine injection

Image source: Getty Images.

To be certain of this, AstraZeneca has started dosing up to 30,000 Americans with AZD1222 or a placebo. If an interim analysis in the fall shows that patients who received the vaccine were at least 50% less likely to get COVID-19, the U.S. Food and Drug Administration could grant AZD1222 an emergency use authorization (EUA) before the end of the year.

AstraZeneca is using up to $1.2 billion in funds provided by the U.S. government to mass-produce AZD1222 in bulk right now, so plenty of doses can be ready for use moments after a potential EUA announcement is made.

In late July, BNT162 from Pfizer and BioNTech and mRNA-1273 from Moderna began phase 3 trials. The AZD1222 program is the third to begin phase 3 clinical trials in the U.S., but it's arguably further ahead than the first two that crossed this hurdle.

In late June, a 5,000-patient phase 3 trial with AZD1222 began in Brazil, an ideal location to run a coronavirus vaccine study. Worldwide, Brazil has suffered from more cases of COVID-19 than all countries but one, the U.S.