My spelling needs work. Herd immunity is the mechanism by which vaccination attains its effectiveness, they are notably only truly effective when everyone is vaccinated. This is why people not vaccinating their children put everyone elses children at risk. It only takes one weak link to break the chain. The human immune system is only so good. Its not like one becomes a super hero against a foreign agent just because of some antibodies. Even in a fully vaccinated population it is possible to contract the disease you are vaccinated against, the likelihood will be small, and its spread will be minimal due to herd immunity. It's just how biology works.
Sure pesticides, okay. It's all a matter of concentrations. A lot of things could be used as pest control in the correct concentrations. Well what else is it in the water for? Mind control? Perhaps it convinces us all that the world in round.
How old are you?