Whether to keep, modify or redirect those orders is a question with significant implications, not just for the nation’s efforts to contain the virus but also for how soon the pandemic can be brought to an end. Of the vaccine doses given globally, about three-quarters have gone to only 10 countries. At least 30 countries have not yet injected a single person.

And global scarcity threatens to grow more acute as nations and regions clamp down on vaccine exports. With infections soaring, India, which had been a major vaccine distributor, is now holding back nearly all of the 2.4 million doses manufactured daily by a private company there. That action follows the European Union’s decision this week to move emergency legislation that would curb vaccine exports for the next six weeks.

Biden administration officials who are inclined to hold on to the coming U.S. surplus point to unmet need and rising uncertainty: Children and adolescents are still unvaccinated, and no one is certain if or when immunity could wear off, which could require scores of millions of booster shots.