When the human immune system is exposed to a disease once, it can develop the ability to quickly respond to a subsequent infection. Therefore, by exposing an individual to an immunogen in a controlled way, their body will then be able to protect itself from infection later on in life.
More on [ Immunization ]

Immunisation - The Safest Way to Protect Your Child - Offers general information about vaccinations and the various diseases concerned. Includes frequently asked questions, links and news.
Meta Description: [ A comprehensive and carefully researched information website about immunisation, vaccines and the diseases they protect against ]
Medinfo: Immunisations - Basic information about the MMR, Meningitis C and Polio vaccines, including reasons for giving, and side effects.
Meta Description: [ Information for patients about immunisation and vaccines. ]
MMR - The Facts - Provides a range of information, including basic questions, a searchable library, and printable resources. Also offers an opportunity to ask the panel specific questions.
Recommendations for Immunisations - A brief look at each vaccine, and the diseases concerned.
Meta Description: [ A list of current recommendations for immunisation: iVillage ]
Surgery Door - Immunisation - Includes common questions, and details about each vaccine.