Please don't waste my time with covid-19 conspiracies and all that stupid shit. I'm not here to talk about people being paranoid of vaccines, I'm just curious about a specific question regarding immunity (which may or may not be retarded anyway. Apparently, a lot of people with doctorates don't get my question when I ask it or don't have an answer, so I can't guarantee this isn't just "schizo-posting" or me overthinking something into oblivion).

And I'm not paranoid. I have no fear-based or ulterior motivation in asking this question, so please if you're about to say something stupid that might belong on /x/ or /pol/ please just do me a favor and shut the fuck up right now. This is a question broader than covid.

So, when you get a (general, normal) vaccine, you become "immune" to a disease, right? Okay. But, they also say the vaccine helps "fight off" the virus.

So how is it that people can spread a disease, like when the conquistadors came to the Americas? If your immune system fights off the disease, does that not mean the disease is killed?

How would you spread a disease if it is dead in your body? Or does the body simply reduce the number of pathogens to some sub clinical level or something?

And how then does a disease get eradicated?
Does anybody even know? I tried asking my sister (who has a doctorate) and even a nurse while waiting for my doctor and they don't seem able to sate this nagging question I have.