How strong is the immune system?

First of all I need to apologize for not posting anything on the blog in some time but at this moment I am so sick that I can barely do anything.
It all started last week Wednesday and has been no better since. Having Bronchitis is not nice and I have it so bad, can't remember when last was I so sick. Yes I do get the odd cold and runny noise but it never goes into my chest & lungs as currently.

What worries me is that it is not getting better and I don't even want to think about when I can start training again as it just upsets me. Today was my first day back at the office and I've rested now for 4 solid days and I don't see any light at the end of the tunnel yet. I am now almost done with the second set of antibiotics.
On the positive site the doctor said that if I wasn't that fit and healthy I would most likely be in hospital now and I must thank my Immune system for that. That brings me to the question, how strong is my immune system?

I eat very healthy, consider myself very healthy with all the training and I do take enough but not too much Vitamins, including Moducare which is an immune booster.

One can say yes the Doc is right could have been worse but can one protect yourself 100% against these flu viruses? Is there a special "recipe" for endurance athletes to protect themselves and does it depends on the environment you find yourself in.

Surely I am not the only one that starts training at 4am and have all types (healthy and not so healthy) of people all day in and out of my office and then finish some nights at 10pm with the training.
All these questions pop up in my head, Do I get enough sleep, Do I eat enough/right, Does my body get enough time to recover?

I first need to recover 100% and then I need to liaise with my coach, www.markallenonline.com to adjust if necessary my training plan. I was 5 weeks into my 20 week program and I was just feeling that I am getting somewhere. Hopefully this won't push me back too much.