[watwut]

Yes some diseases were eradicated that way. Not all of them and we keep vaccinating.

Herd immunity means the disease wont cause epidemic, if it comes from elsewhere. It does not mean that no single person will get the disease if he encounters it.

Notably, flu vaccine did not stopped flu entirely, is the most common yearly vaccine and I really never seen anyone claim it 100% stops flu.

[picofarad]

Oh, you made a category error, I think. Flu has variants and they sometimes "predict" which variant to prepare for incorrectly, but as far as I am aware the flu vaccine is very effective against the correct strain.