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Well, let's see… say you had 2000 participants in the trial, 1000 with a junk vaccine, and 1000 with placebos. Furthermore, let's say you had 200 infections, s
by Eric_WVGG 6y ago
Well, let's see… say you had 2000 participants in the trial, 1000 with a junk vaccine, and 1000 with placebos.
Furthermore, let's say you had 200 infections, split equally between the junk and the placebo.
So yeah, 100 / 200 = 50% effective. A coin toss, which is to say, no better or worse than not getting the vaccine.
Again, this isn't measuring "what one would expect" (how many vaccinated people, exposed to the virus, get the disease), it's "what proportion of vaccinated people get sick relative to unvaccinated people." (again IANAD)
- StavrosK 6y agoKind of seems odd, given that you can never have 0% efficacy (unless your vaccine somehow caused every vaccinated person to get the disease instead of a non-vaccinated person). It seems like you're wasting half your "spread", basically. If you measured efficacy as "1 - (vaccinated infections / unvaccinated infections)", it would be much more intuitive, and you could even get a bit of negative efficacy in the case where your vaccine did nothing.
- iggldiggl 6y agoNo, 50 % means the infection rate (or whatever you're actually measuring) in the vaccine group is half that of the control group. In your example the infection rate are exactly the same, giving an efficacy of 0 % (± whatever confidence interval the size of your trial and placebo groups gives you). See e.g. https://blogs.sciencemag.org/pipeline/archives/2020/09/21/the-vaccine-protocols https://blogs.sciencemag.org/pipeline/archives/2020/09/21/th...