The vaccines and boosters were developed to combat the very early COVID infections. They did a fine job until the virus began mutating and the vaccines (and boosters) became less effective to the point we are at now that they DO NOT prevent contracting the new variants. I suspect that the new variant are not anywhere as lethal as the original strains and thus people are usually having very mild symptoms. Therefore, it seems plausible that the vaccines are not really doing anything at this point. I know many non-vaccinated people that contracted COVID recently that had symptoms similar to vaccinated people.
My doctor said to not get the 4th booster but instead wait until the fall when a new vaccine should be available to combat the most recent COVID variants.
I know, there will always be exceptions but in general, I feel this is the case.