Moderna’s vaccine effort stands in contrast to two other high-profile projects that the United States had hoped would build up its supply: one from the pharmaceutical companies Sanofi of France and GlaxoSmithKline of Britain, and another from the British-Swedish drug maker AstraZeneca and the University of Oxford. For people 65 and older, the trial provided an estimated efficacy of 86.4 percent, lower than the overall estimate of 94.1 percent. So far, two potential differences between the Pfizer-BioNTech and Moderna vaccines have emerged in the F.D.A.’s reviews, but the findings may reflect a shortage of data rather than genuine distinctions. 