Vaccinations are not always effective, nor are they permanent. They are a statistical firebreak against an epidemic. Think of vaccinations like transistors.

Vaccinations are not always effective, nor are they permanent. They are a statistical firebreak against an epidemic. Think of vaccinations like transistors. They are modelled as 1 (vaccinated, won't get sick) or 0 (unvaccinated), but that's not the reality. The reality is very few people have an immunity level of 1.0 (won't get sick) on that scale even after vaccination, and some of those who do seem completely immune are that way because their immune system is particularly good at making a particular disease asymptomatic, not (necessarily) because they were vaccinated. You can still get infected even if you were vaccinated recently. Many vaccinations lose effectiveness after a decade or two at most. Most adults (who are less affluent/wealthy or who don't travel) don't get re-vaccinated for most things because they're at lower risk. The highest risk is in places like preschool, daycare, grade school and college with lots of people in close proximity, and some poor hygiene mixed in. And hospitals and doctors offices. Anti-vaxx parents put everyone else at disproportional risk, because children are a prime infection distribution hub for all kinds of contagious diseases.