My wife is in her 30s and never once had a vaccine. She never gets sick either. This "herd immunity" doesn't need to be 100%, there's a little play, or vaccines aren't as an important role as they like you to believe. Observation is science, while christian science is praying away what you already have. What does she have? What do my kids have? It's all scare tactics.
This is their logic, "well, immmm, uhhhh. Hmmm. You know, if that person who you got it from had been vaccinated, even though you're vaccinated, he wouldn't have gotten it. Maybe! So maybe you wouldn't have too. Go get a booster!"
Epidemiology isn't science anymore than meteorology. "It's raining now, it'll rain for at least an hour more. Let's all do a dance to the Popobawa and pray away clear skies. Go rain go!"