Sophrosyne
Registered User
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I am not confusing anything about efficacy or effectiveness.
With respect @Sunny, you are mistaken about the efficacy rate.
Lets take 2 trial examples, each has 200 participants, half of whom are vaccinated.
Example 1
Infected | Infection rate | ||
Unvaccinated | 100 | 100 | 100% |
Vaccinated | 100 | 3 | 3% |
Reduction % | 97% |
Therefore vaccine reduced the infection rate by 97%
The efficacy formula is arrived at by dividing the reduction %, 97% by the unvaccinated rate, 100% = 97%.
So, in this case, the efficacy rate and the vaccine reduction rate are the same because all of the unvaccinated became infected.
Example 2
Infected | Infection rate | ||
Unvaccinated | 100 | 65 | 65% |
Vaccinated | 100 | 3 | 3% |
Reduction % | 62% |
In this case the vaccine reduced the infection rate by 62% but the efficacy rate is higher.
The reduction rate is 62%, but the efficacy rate, (62% divided by 65%) is 95%, because it takes account of the 35 unvaccinated who did not become infected.