How does the body acquire active immunity to a disease without getting it?

B and T cells: Foreign antigens such as bacteria or viruses stimulate B lymphocytes to produce antibodies against them .T cells produce cytokines that are toxic to them. The body has a memory for these for future attacks that can last weeks to permanent. Often these circulating antibodies can be tested or skin tests developed for specific infections. These are our defenses.

Vaccination: Vaccination can stimulate body to acquire active immunity to a disease without gettiing it, such as MMR.