In general, the flu vaccine is
very effective in preventing the flu or its complications. The effectiveness of
the flu vaccine may vary each year depending on which flu strain is
circulating. It may also be less effective in frail or older persons who have
impaired immune systems. This year, researchers have estimated the flu vaccine
to be 62 percent effective against the flu. While the flu vaccine is not
100 percent effective, it is important to remember that no medical therapy is and it is still important to get the flu vaccine.