A biological preparation that provides active acquired immunity to a particular disease is known as a Vaccine. Vaccines contain a microorganism in a weakened or killed state, or proteins or toxins from the organism. Vaccines can be prophylactic or therapeutic. The World Health Organization (WHO) reports that currently, licensed vaccines are available for twenty-five different preventable infections. For example, vaccines that have proven effective include the influenza vaccine, HPV vaccine, and chicken pox vaccine.
Immunization is an advanced process that triggers the body's immune system to fight against infectious diseases, by the administration of a vaccine. The administration of vaccines is called vaccination. Herd immunity can be when a sufficiently large percentage of a population has been vaccinated.