Any vaccine makes someone immune by injecting a weaker version of the virus/disease into your body, when you inject someone with the disease your body automatically reacts and goes to sort out the invaders. You body creates specific anti-bodies which are chosen for the specific job and when they have finished their job of killing the invaders there will always be one cell with the correct information on it to react straight away, so when a invader invaders for real your body can instantly snap on and kill it before there are any affects to your body
