Most vaccines, such as those for MMR, tetanus, diphtheria, polio, HIB, and even varicella, are very effective and provide a strongly positive health benefit in relation to the risks.
Seasonal influenza vaccines, not so much...
Very true Oblomov, but those statistics showing markedly decreased effectiveness of flu vaccine in those who have been previously vaccinated against other strains are concerning - if true. They suggest something worse than lack of effectiveness. They suggest a blunting of the immune response - along the lines of what allergists are attempting to do with desensitization. That said, I would have to see a lot more data from credible sources.