system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: If I am/my kids are vaccinated why should I be afraid of those who are not vaccinated?

Vaccination should prevent people from getting sick, so why are people so freaked out that some of these diseases are back?  Maybe I just don't understand how vaccinations work.
gpt
It's about something called 'herd immunity'. Basically the principle is that if you have 95% of a population vaccinated against something, then effectively the disease cannot penetrate that population because it won't have enough people to spread to. 

In the short term, if you're vaccinated then no, you don't need to be worried about catching the virus - but what happens if that virus manages to penetrate the population because not enough people were vaccinated against it for herd immunity to work? Still, you're safe because you're vaccinated. Problem is, the virus has now penetrated the population and can evolve and mutate in such a way to bypass your vaccine, and since vaccines take a long time to develop there probably won't be a new vaccine for the new strain before you become infected yourself.