Based on the encouraging findings, the agency intends to grant emergency authorization for use of the vaccine on Friday, people familiar with the F.D.A.’s plans said. The decision would give millions of Americans access to a second coronavirus vaccine beginning as early as next week.

The review by the F.D.A. confirms Moderna’s earlier assessment that its vaccine had an efficacy rate of 94.1 percent in a trial of 30,000 people. Side effects, including fever, headache and fatigue, were unpleasant but not dangerous, the agency found…

Distribution of about six million doses could then begin next week, significantly adding to the millions of doses already being shipped by Pfizer and BioNTech, the companies that developed the first coronavirus vaccine given emergency clearance just last Friday. Health care workers received the first shots on Monday of the Pfizer-BioNTech vaccine, which has an efficacy rate of 95 percent.