Eating healthy, working out consistently, getting enough sleep - that should be enough to keep you from getting sick right? How I wish that were true. However, It definitely promotes a solid immune system - something we as responsible human beings should strive for.
Even with that type of lifestyle, people still get sick. I'm not a proponent of getting the flu shot, but I do believe in being active in your recovery. Here's a quick video on "A Roadmap to Viral Infection Independence."
Stay healthy :)