The new vaccine’s 72 percent efficacy rate in the U.S. clinical trial site — a number scientists have celebrated — falls short of the roughly 95 percent rate found in studies testing the Moderna and Pfizer-BioNTech vaccines. Across all trial sites, the Johnson & Johnson vaccine also showed 85 percent efficacy against severe forms of Covid-19 and 100 percent efficacy against hospitalization and death.

“Don’t get caught up, necessarily, on the number game, because it’s a really good vaccine, and what we need is as many good vaccines as possible,” Dr. Anthony S. Fauci, the government’s top infectious disease expert, said in an interview on Saturday. “Rather than parsing the difference between 94 and 72, accept the fact that now you have three highly effective vaccines. Period.”

If Johnson & Johnson’s vaccine would have been the first to be authorized in the United States instead of the third, “everybody would be doing handstands and back flips and high-fives,” said Dr. James T. McDeavitt, dean of clinical affairs at the Baylor College of Medicine.