Why Professor Frazer has nailed it., page-9

I think you've missing the relevance of the 90% result here.

There were 20 trial participants, five of which were given placebos.

If 15 patients experienced a 100% success rate with the vaccine then that's perfect.

Of the remaing five that were given placebos we could expect at best half to demonstrate better and half to demonstrate worse results than they usually do (over the short time of the phase 1 trials). So maybe two or three demonstrated an improvement.

We could hope that all of the 15 given the vaccines demonstrated improvements plus two or three apparent improvements from the participants given placebos equals 17 or 18 (I.e. 85 or 90 per cent). Take out the placebos and this equates to 100% success rate for the vaccine takers!