The United States has secured almost a third of AstraZeneca’s one billion possible COVID-19 vaccine doses by pledging up to $1.2 billion, as the world’s biggest powers scramble for medicinal supplies to get their economies back to work. “This contract with AstraZeneca is a major milestone in Operation Warp Speed’s work toward a safe, effective, widely available vaccine by 2021,” U.S. Health Secretary Alex Azar said.