AstraZeneca said its vaccine candidate was up to 90 percent effective, suggesting that the world could eventually have at least three working vaccines. At the same time, the virus is accelerating across the U.S., and officials are imposing new restrictions to flatten the curve.AstraZeneca said its vaccine candidate was up to 90 percent effective, suggesting that the world could eventually have at least three working vaccines. At the same time, the virus is accelerating across the U.S., and officials are imposing new restrictions to flatten the curve.NYT > World News