Average Dumb Guy
I am not a doctor, and the Spin gets confusing. For instance, efficacy and effectiveness. A vaccine with an efficacy of 57% (based upon a trial Group of 20 000) means; that of the 10 000 non-placebo trialist, 57% of them didn’t get sick (5700 not sick, but 4300 still became sick). The effectiveness is a separate point all together. It could be 50% to 100% effective. But even if it is 100% effective, this means that it will only protect 57% of those that get it (I am assuming that the placebo people of the trial are not included into efficacy modelling). We have a government telling people that the vaccine is 100% effective in preventing death. When its efficacy is only 57%…
Guy who knows allot more than Average Dumb Guy
Hi. I am a doctor, with training in Epidemiology. Conventionally, the difference between effectiveness and efficacy is just a matter of the setting. An intervention is efficacious if it does what it is supposed to do in an ideal situation, like in randomized clinical trial, where all variables are controlled. An intervention is effective if it does what it is supposed to do in a “real life” situation. That is why many interventions that may have a high efficacy, may not be quite effective. How we calculate both is something that people sometimes do not understand. In order to calculate either, we need to compare the outcomes of those treated with those untreated. For example, if only 5% of vaccinated individuals get sick, that does not mean that the vaccine is 95% effective (or efficacious). Maybe, 5% of unvaccinated individuals also get sick. Since the risk of infection is the same in both groups, the efficacy of the vaccine (in this example) would be 0%. The way we calculate efficacy or effectiveness of any intervention is: (risk in untreated — risk in treated) /(risk in untreated). It is also called “Relative Risk Reduction” (RRR). (edited)
To illustrate, the approximate numbers I remember from the Pfizer vaccine trial were something like the following: the trial included ~ 44,000 subjects, 22,000 in each group (vaccine and placebo). In the vaccine group 9 subjects became sick versus ~ 160 in the placebo group. Since the denominators are equal, we can estimate the efficacy as: (160–9) / 160 ~ 95%. (edited)
Average Dumb Guy
But now this brings up the following question (pls forgive, I ask allot of them). If the virus is fatal to a small percentage of vulnerable and old. And 99.97% of people are okay (a massive portion of them don’t even know they are infected) then how can this vaccine be declared anything without the trials being done on the 0.03% at risk populace?
To me it is pointless testing a vaccine on a healthy group of people. They most probably would not respond the same way as the old and vulnerable set of people.
Guy who knows allot more than Average Dumb Guy
That is an important point. That is why when we define efficacy (or effectiveness, or RRR) we need to define what is the risk that we are trying to reduce. Do we want to measure the RRR of infection? … of getting sick? … of dying? When they did the Pfizer clinical trial, the outcome was the development of symptomatic illness confirmed with laboratory. I don’t think anyone has measured whether the vaccine reduces the risk of dying from COVID-19. That would take a more complicated study.
Average Dumb Guy
And this begs the question of why a vaccine at all? Less than 1% of ppl have a real problem with the virus. And that tiny percentage are not being used in tests. Or the vaccine is not being specifically designed for those who need it most. And, if the tests show any efficacy or result on those who are strong and don’t need them. It means nothing for those who do. If they had to run trials on the actual risk groups, allot of them could die or have no immune response at all (also hyper immune response). And then in a clinical setting the vaccine would never make it out to the public. But the way it has been done, makes it okay to pump out millions into the world.
