This is the best tl;dr I could make, original reduced by 84%. (I’m a bot)
These two studies were substantially different from one another: They didn’t have standardized dosing schemes across the trials, for one thing, nor did they provide the same “Control” injections to volunteers who were not getting the experimental Covid vaccine.
The company also says it will use the data to apply for emergency use authorization in the US. The Food and Drug Administration’s guidance for Covid-19 vaccines does allow for emergency use authorization based on interim analyses, but the same document says this must be supported by a minimum level of vaccine efficacy “For a placebo-controlled efficacy trial.” Again: it refers to a trial.
How did Oxford-AstraZeneca end up with this patched-together analysis instead of data from a single, large trial?