In the 1970s the fortunes of the world economy, in all its unfathomable complexity, seemed to turn on one product: oil. Exported by a narrow clique of countries, this vital input was hostage to ferocious political forces. Today the world’s economic prospects similarly depend on another all-important input, vaccines, which are also narrowly produced, delicately political—and unevenly distributed. Widespread vaccination is helping America to boom. But delays in buying, making and deploying shots have left much of the world vulnerable to new virus outbreaks and economic setbacks.