Dr. Seth Berkley, the chief executive of Gavi, the nonprofit at Covax’s heart, said insufficient early financing made supply shortages inevitable. When distribution problems of the type in Chad and Benin emerge, Covax tries to “move those vaccines to other countries, but then to work with those countries to try to improve capacity,” he said.

Supporters and critics agree that the program must improve, rapidly. As of early July, confidential Covax documents indicated that 22 nations, some with surging fatalities, reported being nearly or entirely out of doses from the program.

“The way Covax was packaged and branded, African countries thought it was going to be their savior,” said Dr. Catherine Kyobutungi, who directs the African Population and Health Research Center. “When it didn’t meet expectations, there was nothing else.”

In the frantic early months of 2020, health experts strategized on how to equitably inoculate the world. Covax was the answer, bringing together two Gates-funded nonprofits, Gavi and the Coalition for Epidemic Preparedness Innovations, or CEPI; the World Health Organization; and UNICEF, which would lead delivery efforts. It hoped to be a major global vaccine buyer, for both rich and poor nations, giving it the clout to bully vaccine makers.

But if rich nations pledged donations, they did not make obliging partners. Britain negotiated for wealthier participants to be given a choice of vaccines to purchase through Covax, creating delays, said Kate Elder, senior vaccines policy adviser for Doctors Without Borders’ Access Campaign.

Most important, rich nations became rivals in a vaccine-buying race, paying premiums to secure their own shots while slow-walking financial pledges that Covax needed to sign deals.