In their announcement of the results, Pfizer and BioNTech revealed a surprise. The companies said they had decided not to conduct the 32-case analysis “after a discussion with the FDA.” Instead, they planned to conduct the analysis after 62 cases. But by the time the plan had been formalized, there had been 94 cases of Covid-19 in the study. It’s not known how many were in the vaccine arm, but it would have to be nine or fewer.

Gruber said that Pfizer and BioNTech had decided in late October that they wanted to drop the 32-case interim analysis. At that time, the companies decided to stop having their lab confirm cases of Covid-19 in the study, instead leaving samples in storage. The FDA was aware of this decision. Discussions between the agency and the companies concluded, and testing began this past Wednesday. When the samples were tested, there were 94 cases of Covid in the trial. The DSMB met on Sunday.

This means that the statistical strength of the result is likely far stronger than was initially expected. It also means that if Pfizer had held to the original plan, the data would likely have been available in October, as its CEO, Albert Bourla, had initially predicted.