What the immune system is.

The immune system keeps track of every microbe it has ever defeated. This means it can remember and destroy the microbe faster than when it first entered your body and before it can multiply and make you fell sick again. Your immune system is stronger when you are young. The immune system does not work as good when you get older. Catching a cold or flu doesn’t give you immunity to other viruses! Now you know what the immune system does when it enters your body.