Also Read | Covid vaccination faces slow startThe setbacks, which come on the eve of a decision from regulators whether to recommend the shot for use in Europe, suggest AstraZeneca is falling behind in the vaccine arms race.
The company has relatively little experience in vaccines, a tricky, typically low-margin niche in the global pharmaceuticals industry.
The manufacturing process the company uses, piggybacking on a chimpanzee cold virus, can be more difficult to quickly scale up than the one employed by Pfizer Inc.