I agree that attending large events is a type of risk compensation, and we may be referring to similar behavior patterns using different words here. But I’m trying to distinguish between these two types of infection:
Infections resulting from people going about their daily activities (e.g. getting exposed at work, in a store or restaurant, other small gatherings, etc.) Here, individuals might indeed change their behavior based on their own vaccination status and risk tolerance. But since Omicron is so widespread at this point, the probability that an infected person was vaccinated should be close to the base rate of vaccination among the overall population (although somewhat lower, since the vaccines still prevent some transmission of Omicron). In other words, P(vaccinated | type-1 infection) is a little less than P(vaccinated).
Infections resulting directly from attending large superspreader events where proof of vaccination was required. In this case, while P(vaccinated | type-2 infection) won’t be exactly 1 due to the possibility of fake vaccine ID cards or weak enforcement of the policy at the event, I think it would still be quite close to 1.
If type-2 infections are a high enough percentage of overall infections, this could make it look like vaccinated people are more likely to get infected (which would be true at the population level!) even though getting vaccinated makes it less likely for any individual to get infected (assuming their behavior after vaccination remains the same).
Apologies if much of this is obvious or redundant—I’m still trying to understand the gears behind this dynamic better myself. I agree there is likely a component coming from “vaccinated people take on more risk in general”, but I hadn’t considered that policies which only allow vaccinated people (to a first approximation) to attend large potentially-superspreading events could lead to increased transmission among the vaccinated relative to the unvaccinated, which could lead to negative perceived vaccine effectiveness, until seeing Peter’s post.
I agree that attending large events is a type of risk compensation, and we may be referring to similar behavior patterns using different words here. But I’m trying to distinguish between these two types of infection:
Infections resulting from people going about their daily activities (e.g. getting exposed at work, in a store or restaurant, other small gatherings, etc.) Here, individuals might indeed change their behavior based on their own vaccination status and risk tolerance. But since Omicron is so widespread at this point, the probability that an infected person was vaccinated should be close to the base rate of vaccination among the overall population (although somewhat lower, since the vaccines still prevent some transmission of Omicron). In other words, P(vaccinated | type-1 infection) is a little less than P(vaccinated).
Infections resulting directly from attending large superspreader events where proof of vaccination was required. In this case, while P(vaccinated | type-2 infection) won’t be exactly 1 due to the possibility of fake vaccine ID cards or weak enforcement of the policy at the event, I think it would still be quite close to 1.
If type-2 infections are a high enough percentage of overall infections, this could make it look like vaccinated people are more likely to get infected (which would be true at the population level!) even though getting vaccinated makes it less likely for any individual to get infected (assuming their behavior after vaccination remains the same).
Apologies if much of this is obvious or redundant—I’m still trying to understand the gears behind this dynamic better myself. I agree there is likely a component coming from “vaccinated people take on more risk in general”, but I hadn’t considered that policies which only allow vaccinated people (to a first approximation) to attend large potentially-superspreading events could lead to increased transmission among the vaccinated relative to the unvaccinated, which could lead to negative perceived vaccine effectiveness, until seeing Peter’s post.
Thank you, good explanation. But see also my response to tivelen below.