Pfizer's clinical trial showed 95% efficacy as a "relative risk reduction" when researchers checked the clinical trial data (which FDA wanted to withhold for 55 years but a Texas judge ordered its release) , for the actual risk reduction it was shown to be a negative value. Here is one resource on the subject https://www.pandata.org/understanding-relative-risk-reductio... I tried to find a better reference but can not find the exact one I'm looking for which came from a Canadian university (ryerson I believe)