It's still flu season, but a preliminary report by the US Centres for Disease Control suggests this year's flu shot is nearly 50 per cent effective at reducing a person's chance of getting sick. This is actually pretty good considering that, just two years ago, the flu shot's effectiveness was down at a paltry 19 per cent. Here's why the flu shot varies so widely from year to year -- and why you should get a shot this year if you haven't already.