The immune system is our defense system for recognizing and eliminating infections or "foreign invaders." It is made up of a network of specialized cells and organs. When the immune system is functioning properly, it can tell the difference between foreign invaders and the bodys own cells and will create a response to eliminate or neutralize the invader. There are different types of immune responses, those we were born with (innate immunity) and those we learn (acquired immunity).
When we get sick, some of the symptoms we experience such as fever or rashes are actually caused by our immune system's attack on the invader. The time it takes for our body to recognize and respond to a new infection generally takes several days. Once a robust and effective response has been learned, the immune system will attack and control the infection. If our body confronts that specific infection again the learned (acquired) responses swiftly kick into high gear and contain it before it causes a problem. This immunologic memory of how to fight a disease is stored in what are called memory B cells and/or memory T cells. In general, once a specific (HIV or other) immune response has been mounted, that response becomes part of our immunologic memory.
A vaccine is a substance that teaches the immune system how to recognize and defend against bacteria and viruses that cause disease. Vaccines are made by using the same components that are found in the natural virus or bacteria, using made man materials, or a combination of both. A vaccine is not a cure, but can prevent infection or slow disease progression.
One example is the flu (influenza) vaccine. Just before flu season comes around many people get a flu shot (vaccine). This is a severely weakened form of the flu virus, or a man-made flu virus particle that prompts an immune response without causing disease. The weakened or man-made particle is mixed in with something that helps to stimulate our cells to respond. Sometimes this response causes a mild fever, swollen joints or stiffness, which are common signs that the immune system is doing something. When flu season arrives, the flu vaccine should have armed your immune system to respond to the new flu virus so that it is controlled and you will not experience symptoms of the flu. Once an immune response has been learned, it can be a swift and potent first line of defense against disease.