That's probably one reason. There's just something about vaccines that makes people unreasonably paranoid though. I once saw a person about to get an infusion of a pretty dangerous immuno suppressing drug. They had a bad disease, it was worth the risks. They didn't seem all that concerned though. Before the infusion could happen there was a requirement to get a few vaccines. You know, to help prevent getting seriously ill while you're immuno suppressed. The vaccines won't work after the infusion, only before. Person fought their doctors for months refusing any vaccines before finally giving in, getting the vaccines, and finally getting the drug they need.