Describe what happens when a person receives a vaccine

Question

osprey · Answer

I heard this some time ago on TV. 
In the case of vaccination against smallpox, people who got "cowpox" were found to not get smallpox. So, a scientist decided to use part of the cow-person system as a medicine and see if it protected people from smallpox. And, they found that it did. And so they tried "vaccinating" people to prevent them getting the lethal smallpox. Vaccinate comes from the Latin (old Italian) word "vax" for "cow".
It COULD be that "vaccination" basically "poisons" the body by a VERY SMALL AMOUNT and "educates" the body's immune system to produce the anti bodies to kill the invader. 
I hope I got this right .... I'm no expert.