At first glance, the results reported Friday from the long-awaited trial of Johnson & Johnson’s coronavirus vaccine might have seemed disappointing. Its overall efficacy — the ability to prevent moderate and severe disease — was reported at 72% in the United States, 66% in Latin American countries and 57% in South Africa.

Those figures appear far below the high bar set by Pfizer-BioNTech and Moderna, the first two vaccines authorized for emergency use in the United States, which reported overall efficacy from 94% to 95%.

Dr. Anthony Fauci, America's leading infectious disease expert and now the lead medical adviser to U.S. President Joe Biden on the coronavirus pandemic, acknowledged the striking difference at a briefing Friday.