Active immunity develops when the body manufactures its own antibodies following exposure to an antigen. Active immunity may occur naturally as a result of exposure to foreign antigens or artificially via vaccinations.

Passive immunity is produced by transferring antibodies from one individual to another. One example of passive immunity is when maternal antibodies cross the placenta and provide protection to the fetus. Maternal antibodies are also passed from mother to infant during breastfeeding. Artificial passive immunity occurs when antibodies are injected into the body. Passive immunity is used to treat rabies, tetanus, and rattlesnake bites.