Vaccination's the administration of antigenic material (the vaccine) to produce immunity to a disease. Vaccines can prevent or ameliorate the effects of infection by a pathogen. Vaccination's generally considered to be the most effective and cost-effective method of preventing infectious diseases. The material administrated can either be live but weakened forms of pathogens (bacteria or viruses), killed or inactivated forms of these pathogens, or purified material such as proteins. Smallpox was… (More on Vaccination)