system
Given the following post, respond as if you're commenting on Reddit:
human
Why is not vaccinating some children a threat to the whole population and not just other unvaccinated people?

I've heard that people not vaccinating their children is a threat to herd immunity, but I don't quite understand how someone getting sick would be a threat to the majority of people that are vaccinated.
gpt
Vaccines are not 100% effective. You could get the vaccine, and still get sick.

Some people cannot take vaccines because of allergies or complicating medical problems. Very young children cannot be vaccinated for some diseases because their immune systems aren't strong enough. If a patient comes into the hospital with a harmful disease, that child could die. These populations are at risk because there are people purposefully keeping diseases that should be eradicated completely (and in some cases, were) alive.