> this means 34% of vaccinated people develop a covid infection That's not what "effective" means. It means that if your probability of getting infected witho

> this means 34% of vaccinated people develop a covid infection That's not what "effective" means. It means that if your probability of getting infected without the vaccine is p, your probability of getting infected with the vaccine is .34*p. One way to think about it is that the "ineffectiveness" is the relative risk P[infected|vaccinated]/P[infected|unvaccinated], and effectiveness is 1-ineffectiveness. A vaccine can be 100% effective even if P[infected] is negligible. P[infected] is per unit time and does not account for the dynamics of the situation. For example, if the vaccine is not powerful enough to make R<1, then everybody becomes infected eventually regardless of the vaccine.