Dialogue with a Friend about Vaccines

by RG

Friend: “I got my first shot today.”

Me: “How are you feeling about that?”

Friend: “Great! We all have to do our bit and I’m looking forward to things getting back to normal.”

Me: “So, I assume you feel that the vaccine is safe and effective?”

Friend: “Of course – I wouldn’t take something that wasn’t going to work. You know it’s 95% effective, right?”

Me: “I’ve heard that claim, yes.”

Friend: “What do you mean ‘claim’?”

Me: “I’m aware that the CDC and the vaccine manufacturers are reporting that it’s 95% effective.”

Friend: “So, what’s the problem? 95% is pretty damn good isn’t it?”

Me: “When considering whether or not to take an experimental medical treatment that hasn’t been granted full approval I like to dig a bit deeper into how it was determined to be safe.”

Friend: “Oh yeah, so what did you find when you went ‘digging’?”

Me: “Well one thing that I was surprised to find was just how few people the 95% figure was based on - only 170 people.”

Friend: “Oh wow, that’s not many.”

Me: “Another thing that surprised me was that you only had to exhibit one symptom to be considered a case. The ‘95% effective’ claim is based on the fact that only 8 of the 170 cases occurred in the group that was vaccinated whereas 162 of the cases occurred in the group that was given the placebo. 8 is 5% of 162, hence the claim that it’s 95% effective (100 - 5 = 95).

Friend: “So, what’s the problem?”

Me: “The problem is that it only measures ‘relative’ efficacy based on a very small sample. This way of looking at things doesn’t take into account the total number of people in the trial. There were over 18,000 people who got the vaccine and over 18,000 people who got the placebo. When you compare 8 to 18,000 and 162 to 18,000 you get 0.04% for the vaccinated group and 0.88% for the placebo group. So, the real level of efficacy, what’s called the ‘absolute’ efficacy is the difference between 0.04% and 0.88% which is only 0.84% NOT 95%.”

Friend: “I’m confused. What does this all mean?”

Me: “It means that if you take the vaccine you have about a one percent chance of reducing one symptom – there’s a 99% chance it won’t work.”

Friend: “Are you sure?”

Me: “Yes. Positive.”

Friend: “Can we change the subject?”