Ever wonder how a vaccine works? Well, I will tell ya! [b]Step One -[/b] The first step to any vaccine is its creation. This process can be simple, or complex. However the end result is always the same, a dead, or weakened strain of a virus/bacteria. [b]Step Two - [/b]The virus/bacteria is injected into the human host. The body will almost immediately recognize the invader and begin an immune response. It is during this initial response that the magic happens. Some white blood cells, B cells can recognize invaders directly. But other cells known as T cells need help from cells called antigen-presenting cells. These antigen presenting cells then envelope and combine with the fragments of an invader and human leukocyte antigens. This combination of antigen and HLA molecules moves to the cells surface as a receptor. This then allows a T cell to lock into the now available receptor. The T cell is then activated and is now able to fight of an invader with that specific antigen. [b]Step Three - [/b]The body has responded to the invader. The immune system can remember every antigen encountered because after an encounter, some lymphocytes develop into memory cells. These cells live for years or even decades. There are two main types of memory cells, T cells and B cells. The T cells can be found in thymus where they are produced, and matured. The B cells can be found within the Red Marrow of bone. [b]Step Four -[/b] You have been vaccinated, you happen to run into the same virus a year later, except it is a live virus now. It enters the body, it makes it into the blood stream. An immune response occurs. An antigen presenting cell recognizes the invader. The body begins the same cycle it did before when it encountered the vaccine. However this time the response is FASTER and far more EFFECTIVE. It is because of these memory cells that you become relatively immune. [b]Step Five - [/b]You have been successfully vaccinated. You are protecting not only yourself, but those whom you interact with. Thanks for reading. This was overly simplified and if anyone has any questions feel free to ask.