At first glance, the results reported on Friday from the long-awaited trial of Johnson & Johnson's Covid-19 vaccine might have seemed disappointing. Its overall efficacy - the ability to prevent moderate and severe disease - was reported at 72 percent in the United States, 66 percent in Latin American countries and 57 percent 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 percent.
But Dr. Anthony S. Fauci, the nation's leading infectious disease expert, said that the more crucial measure was the ability to prevent severe disease, which translates to keeping people out of the hospital and preventing deaths. And that result, for Johnson & Johnson, was 85 percent in all of the countries where it was tested, including South Africa, where a rapidly spreading variant of the virus had shown some ability to elude vaccines.