The US study comprised 30,000 volunteers, 20,000 of whom were given the vaccine while the rest got dummy shots. The results were announced Monday.

The early findings from the US study are just one set of information AstraZeneca must submit to the Food and Drug Administration. An FDA advisory committee will publicly debate the evidence behind the shots before the agency decides whether to allow emergency use of the vaccine.

While the AstraZeneca vaccine has been authorized in more than 50 countries worldwide, scientists have been awaiting results of the US study in hopes it will clear up some of the confusion about just how well the shots really work.