Fair. In some years the 'effectiveness' (I have no idea how this is measured) is as low as 25%, when they 'guess wrong' as to what the prevalent strains might b

Fair. In some years the 'effectiveness' (I have no idea how this is measured) is as low as 25%, when they 'guess wrong' as to what the prevalent strains might be. However, it can also reduce symptoms. Shorten the flu, if not eliminate it. All of these things can make a difference at the margins; make a vulnerable person merely sick instead of deadly sick. And most importantly for those vulnerable folks at the highest risk of dying, the vaccine makes them less likely to come in contact with someone who spreads the flu to them in the first place.