Current flu vaccines are between 40% and 60% effective at preventing the disease. And that's only in years where the vacci e is well matched to the prevalent flu variant.
Shouldn't be too hard to improve on that.
I've always defined vaccine as "preventing a person from getting the disease," as opposed to "reducing the severity/symptoms."
Not to pick on Fly320s, apparently a lot of people thought this, but it's a fundamental misunderstanding on how vaccines work. Vaccines and illnesses are not binary get it or don't situations. Vaccines make your immune system better at fighting a pathogen, but a huge dose of pathogen, or wierd variant, or just bad luck can all contribute to you getting a disease anyway.