How is the AstraZeneca vaccine different, and is it safe? Yahoo News Explains

The U.S. has millions of doses of the AstraZeneca coronavirus vaccine, made by the British-Swedish drugmaker in collaboration with Oxford University, sitting in distribution centers. The company has not yet filed for authorization in the U.S.; recent reports suggest it could do so by the end of March. But what is the vaccine? And what is the controversy surrounding it in Europe? Yahoo News explains.