Vaccinations are a dead, inactive form of the virus, bacteria, or toxin which purpose is to prepare the body to defend itself when the actual virus comes. So, when the virus attacks, the body's immune system is ready to kill the virus.References:
http://www.wisegeek.com/how-does-a-vaccine-work.htm
http://www.prisonplanet.com/images/november2007/151107vaccine.jpg
