AProudLefty
He cries for attention. :)
The description you cited was clearly dumbed down so that 3rd graders and people like you could "understand" it, regardless of the source.
No it's so that YOU can understand.
Here's a more accurate definition:
vaccine
[vakˈsēn]
NOUN
a substance used to stimulate the production of antibodies and provide immunity against one or several diseases, prepared from the causative agent of a disease, its products, or a synthetic substitute, treated to act as an antigen without inducing the disease.