It's amazing to me how much medicine is hyped up for keeping us healthy when we have the best defense inside of us.
Sure it's not 100% - but it's got a much better track record than drug interventions. And if you treat it right, your immune system can do an extraordinary job in keeping you healthy.
The key is to nourish it with the nutrients it needs to thrive. Here's a great article listing a number of nutritional immune system boosters: