Pfizer announced today that preliminary results from their phase 3 trial showed their vaccine to be approximately 90% effective.
But how did they calculate a result of 90%?
44,538 participants received 2 injections of the vaccine or a placebo. 94 of those participants developed Covid-19 PLUS at least one symptom, and only 9 of those 94 had received the real vaccine.
So while the relative risk reduction is close to 90%, the absolute risk reduction paints a different story and may end up being just around 1%-2%. The official data has not been published nor yet peer reviewed, these estimates are determined from the numbers provided in Pfizer’s press release.
To begin to understand how these numbers are calculated – the difference between relative and absolute risk reduction- I invite you to watch my video “The Absolute Truth About Your Medical Treatment”.
It is important to add that participants in such a trial will not be people with serious pre-existing conditions that are, in the real world, most at risk for Covid-19. Also to note, this trial did not test whether the vaccine can prevent people from still carrying the virus without symptoms.