Is There a Way to Avoid the Flu?

Why is it that many people come down with the flu in winter months but flu is rare in the summer? Why then do new flu strains such as the recent swine flu epidemic affect people even in the summer months? Why is it that the flu shot is often less effect for the elderly? Could it be that there is some factor or factors that allow our immune systems to recognize viruses that are similar but not identical to previously encountered viruses? If this is so, then, if the body had adequate levels o...