How is passive immunity naturally acquired?

Passive immunity is naturally acquired when antibodies produced by one individual are transferred to another individual, providing immediate but temporary protection against diseases. This process occurs during pregnancy when a mother passes immunoglobulin G (IgG) antibodies to her fetus through the placenta. These antibodies offer the newborn some level of immunity against infections that the mother has previously encountered, essentially protecting the infant during the first few months of life when their immune system is still developing.

In contrast, vaccination, though a method of acquiring immunity, involves the introduction of antigens to stimulate the body’s immune response and is classified as active immunity. Exposure to viral infections results in active immunity as the body fights off the virus and generates its own antibodies. Blood transfusions can provide passive immunity but are not a natural method; rather, they involve transfer of antibodies from one person to another through medical procedures, typically used in specific clinical situations.