What statistics tells us about the efficacy of the Pfizer, Moderna, & Oxford vaccines | American Enterprise Institute - AEI

What statistics tells us about the efficacy of the Pfizer, Moderna, & Oxford vaccines--American Enterprise Institute - AEI

"The news that the Pfizer-BioNTech and Moderna vaccines are 95 percent effective at preventing COVID-19 disease...

...While this is certainly welcome news, it requires context, based on the statistical methods used to evaluate efficacy in clinical trials. 

In the case of the Pfizer-BioNTech vaccine, for example, the estimated efficacy is based on 170 observed cases of COVID-19 among trial participants, 162 of whom received the placebo. 

Thus, only 8 trial volunteers who received the vaccine developed COVID-19, which translates into an observed efficacy rate of about 95 percent.

A reasonable question for those trying to understand the implications of the trial, however, is whether this impressive result could have occurred by chance, given that the sample size of 170 cases is relatively small...Read all.