Vaccine Efficacy, Statistical Power and Mental Models



 If that’s what the vaccine trials were measuring—the height of thewall that is our immune system comparing vaccine effectiveness would make a lot of sense.  Many high-profile, highly-credentialed people have been (misleadingly) describing it exactly in that manner: that if a vaccine is 95% effective, those 5% are left “unprotected.” If Moderna and Pfizer and 95% efficacious, and if Johnson and Johnson is 66%—well, that would mean that 34% of the people are left “unprotected.” right?

Wrong. To get to why that assumption is not right—and why those vaccine efficacy numbers are not the height of the wall that represents the immune system—let me first mention something important The two mRNA vaccines do appear to be spectacular, but they were tested under conditions where those pesky “variants-of-concern”—the B.117 (UK one) and B. 1.351 (South Africa) and P1–were not widespread. If tested now, under equal conditions, those numbers may be closer. Plus, Johnson & Johnson is a single-shot with a trial with a booster underway. So those efficacy numbers may well be much closer in reality than they appear from the trial results. But let’s leave that aside for a moment.

Author(s): Zeynep Tufekci

Publication Date: 2 March 2021

Publication Site: Insight on Substack