Based on publicly available numbers, the 95% Bayesian credible interval is roughly 90.5% to 97.6%.

No, you bring up a great question. This kind of vaccine trial is not designed to provide that information, unfortunately. The goal of this study is to show that the vaccine is at least 30% effective (defined by Vaccine Efficacy (VE) in the Pfizer protocol), with a soft goal of hitting a VE of 50%. We don't know anything about what the total population of _possible_ infections in either arm would be.

That said, if we assume that there are in total 170 cases (which is true at this point in time but will change), and that there are 162 cases in the control group and 8 cases in the vaccine group, we can construct a posterior of the VE. Here's an older posterior (done with data from the press releases in the first IA a few days ago) http://blog.fellstat.com/?p=468 that graphs this posterior. There is some uncertainty, but as you can see results are still promising. That said we just don't know how case counts will change, and while it will be fascinating to watch the results change over time, these sorts of tests are just about getting enough data to mark a vaccine as effective, not about trying to extrapolate any larger effect.