What does region mean in this context? A region of the body?
Antigen binding?
Your statement on future infections by a distinct antigen than you were immunized for is objectively true. A vaccine is not a panacea for all viruses.
If I prepare my home for a flood then I shouldn't expect an earthquake to be stopped.
If we are making the case that a surface protein is too targetted then I would point towards the seasonality of the flu.