Days after grabbing headlines with its COVID-19 'vaccine for the world', AstraZeneca is facing tricky questions about its success rate that some experts say could hinder its chances of getting speedy U.S. and EU regulatory approval. Subscribe: http://smarturl.it/reuterssubscribe Reuters brings you the latest business, finance and breaking news video from around the globe. Our reputation for accuracy and impartiality is unparalleled. Get the latest news on: http://reuters.com/ Follow Reuters on Facebook: https://www.facebook.com/Reuters Follow Reuters on Twitter: https://twitter.com/Reuters Follow Reuters on Instagram: https://www.instagram.com/reuters/?hl=en