South Africa, whose scientists detected the variant, has fully vaccinated only 24 percent of its population, according to the Our World in Data project at the University of Oxford. It has a better vaccination rate than most countries on the continent, but has asked vaccine makers to stop sending doses: It is having trouble getting shots into arms, in part because of distribution bottlenecks and in part because many people are hesitant to take them.
The Coronavirus Pandemic: Key Things to Know
Elsewhere in Africa, the vaccination rate is much lower, and in some countries, even health care workers have had trouble getting their shots. The W.H.O. reported last week that just 27 percent of health workers in Africa had been fully vaccinated.
The Biden administration has pledged to donate more than a billion vaccine doses to other nations, and so far it has shipped 275 million doses to 110 countries. The president said, as he has in the past, that the United States has donated more doses than any other nation. He implored other foreign leaders to increase their donations.
â€œNow we need the rest of the world to step as well,â€ he said.
But activists and some global health experts said the administration needed to move faster, arguing that vaccine inequities were the reason for the emergence of the variant.
â€œThis is precisely what experts have been predicting was going to happen â€” that the extraordinary inequities and gaps between low-income countries and high-income countries creates this massive vulnerability, and itâ€™s going to continue to generate these dangerous variants,â€ said J. Stephen Morrison, a global health expert at the Center for Strategic and International Studies in Washington. â€œThat point is glaringly obvious, and itâ€™s painful.â€
Mr. Bidenâ€™s top health advisers, including Dr. Fauci, spent much of the holiday weekend consulting with their South African counterparts.
Dr. Fauci told the president that it would take approximately two weeks to learn more about the variantâ€™s transmissibility and severity, but that â€œhe continues to believe that existing vaccines are likely to provide a degree of protection against severe casesâ€ of Covid, according to a statement from the White House.
Alexandra E. Petri contributed reporting.