The problems start with the fact that Monday’s announcement did not present results from a single, large-scale, Phase 3 clinical trial, as was the case for earlier bulletins about the BNT-Pfizer and Moderna vaccines. Instead, Oxford-AstraZeneca’s data came out of two separate studies: one in the UK that began in May, and another in Brazil, which got started at the end of June. 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 fact that they may have had to combine data from two trials in order to get a strong enough result raises the first red flag.

Consider that leading vaccine makers—including AstraZeneca—issued a scientific-rigor-and-integrity pledge back in September, in which they promised to submit their products for approval or emergency use authorization only “after demonstrating safety and efficacy through a Phase 3 clinical study that is designed and conducted to meet requirements of expert regulatory authorities such as FDA.” Note the wording here: These companies did not suggest that they might claim to have demonstrated efficacy through multiple, distinct clinical studies, combined together to get enough data. They said they would use a Phase 3 study—as in, one big one. Yet AstraZeneca has already applied on the basis of this data for approval in Canada, and has plans to do the same in Britain, Europe and Brazil. The company also says it will use the data to apply for emergency use authorization in the US.