The immune system is designed to keep pathogenic factors from harming the body. It is the moat around our body/castle. In times of health (when the body/castle is safe from invaders), one should build the moat wider and deeper; ie, strengthen the immune system. Herbally speaking, this is the time to use Astragalus, medicinal mushrooms and other herbs which strengthen the immune system.
However, once the barbarians have breached the castle walls and have entered the castle (the body), do you still spend time making the moat wider and deeper? No, you forget about the moat and guard the castle! You get out your spears and hot oil (anti-viral, anti-bacterial herbs) and fight back. Then, once the barbarians are pushed back, you the work on digging out the moat once again (strengthening the immune system).
Many people mistakenly take immune stimulants while sick. This is a mistake. In Chinese medicine, it is said one should use medicinals which push up and out when fighting a bug, thus sweating out the pathogen and ridding it from the body. Many herbs have this function. However, immune stimulants have the opposite effect. Their energies push downward and inward. This is beneficial when trying to strengthen the inner workings of the immune system, but when you are trying to expel a pathogen, this only serves to drive it deeper into the body.
If you get sick, the best time to take herbs is the second you start feeling symptoms. Just as it is easier to repel an invader when he has only one foot in the door, it is easier to expel a pathogen before it has fully taken hold.
In the Dr. Dave's repertoire, the best formula for expelling a pathogen is Throat Zap. When you start feeling sick, or even think you might be feeling sick, you can use Throat Zap every hour or two to knock out the pathogen before it takes hold. No matter your favorite remedy, use it early and use it often at the onset of a cold or flu.
Then, when you are well again, get the shovels out again and start back in on the moat. Remember, it takes time and persistence to achieve measurable results in moat building, but by taking herbs which benefit the immune system, eating in a healthy manner and reducing your stress levels, you will soon find your immune system functioning as well as the deepest, widest moats in the kingdom!