According to Merriam-Webster,
IMMUNITY: the quality or state of being immune; especially : a condition of being able to resist a particular disease especially through preventing development of a pathogenic microorganism or by counteracting the effects of its products
When I typed in immunization it forwarded me to the definition of immunize, which says "to make immune."
If I have been immunized, then why am I not immune? Though my child has not received the MMR vaccine, I did, all of them, before I entered junior high, which was only 15 years ago.
a: a popular belief or tradition that has grown up around something or someone; especially : one embodying the ideals and institutions of a society or segment of society
b: an unfounded or false notion
By purposefully using the words immunize and immunization in place of words like vaccinate or vaccine the medical community, the government, and various other "segments of society" perpetuate the belief that vaccines somehow create immunity to dangerous diseases. That may be the goal but it is not a guarantee. And until it is, it should not be spoken of in that way.