What is the difference between active and passive immunization?

Active immunization stimulates the body's immune system to produce its own antibodies and memory cells through exposure to antigens (via vaccines or natural infection). It takes weeks to develop but provides long-lasting protection through immunological memory. Passive immunization provides pre-formed antibodies from external sources, offering immediate but temporary protection (weeks to months). Sources include: maternal antibodies (transplacental, breast milk), immune globulin preparations (IVIG, specific immunoglobulins for rabies, hepatitis B), and monoclonal antibody therapies. Passive immunization is used for post-exposure prophylaxis, immunocompromised patients, and when immediate protection is needed. Both can be combined (rabies treatment).