How do vaccines prevent disease?

Vaccines introduce an attenuated form of the virus or bacteria into the body.

Explanation:

Vaccines introduce an attenuated form of the virus or bacteria into the body, meaning the virulence of the virus or bacteria has been negated. Introduction of this attenuated form enables the immune cells to easily eliminate the pathogen even without getting diseased and later have memory (in memory B and T cells) so that in case of a real infection, it is easily eradicated.