UNDATED (KDAL) - A new study conducted by the University of Minnesota shows that flu shots may not be as effective as previously thought.  The flu vaccine currently in use across the U-S prevents the flu in about 59 percent of healthy adults who get the shot.  Earlier studies projected that the vaccine protected 70 to 90 percent of those who receive it.  U-M researchers say they're not sure how well the vaccine works in young children and the elderly.  The study notes that a new and improved generation of vaccine needs to be developed to help hold the flu in check.