Quote:
Originally Posted by SailinAway
Does efficacy depend on the number of direct exposures to Covid? I.e., if I got the Pfizer vaccine I have a 5% chance of infection with each exposure? So 100 exposures could result in 5 infections. (I think you explained this in another thread but I've forgotten the answer.)
(Exposure has been defined by the CDC etc. in terms of distance from an infected person and duration of exposure.)
I think you're also saying that my friend's infection is a simple matter of probability, not an indication that the vaccination "didn't take" with her.
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Excellent questions.
For any person, likelihood of getting covid increases with number and intensity of exposures.
Efficacy in the case of vaccines describes the likelihood of getting covid if you've been vaxxed compared to the likelihood of getting covid if you have not been vaxxed. These things assume that every person has the same amount of exposure to virus.
A simplified example-- They give 1,000 people a vaccine, and another 1,000 people a fake placebo vaccine. When 100 people in the placebo group have covid, they stop the trial and count the number of vaxxed people with covid. If the number of vaxxed people with covid is 5, then the efficacy of the vaccine is expected to be 95%. If there are 10 positives in the vaxxed group, then the efficacy is 90%. So no one should be surprised that 5 or 10% of the vaxxed population gets covid--this is basically what the companies and FDA predicted would happen.
In the trial, they are assuming that every person has the same level of risk, and as you'd expect, they give people a bunch of questions to try to control for this. They would throw out a trial if they discovered that a whole bunch of people were partying in P-town or Sturgis, just for example.
So if you get a 95% effective vaccine, you have only 1/20 the risk of an unvaxxed person, and it's really unlikely you're going to get covid at the store or work. But if you go to a mosh pit, especially with a significant number of unvaxxed people, it's kind of like taking a bath in covid, and you are asking for trouble