What is passive immunity?

Passive immunity refers to the type of immunity that is acquired through the transfer of antibodies from one individual to another, rather than being generated by the individual's own immune system. This can occur naturally, such as when a mother passes antibodies to her fetus through the placenta or to her infant through breast milk. These maternal antibodies provide immediate, but temporary, protection to the newborn against infections. This classification is critical in understanding how immunity can be conferred without the individual needing to actively produce antibodies themselves, which is what distinguishes it from other forms of immunity.

Other options relate to different concepts. Immunity developed through vaccination is known as active immunity because the individual’s immune system is stimulated to produce its own antibodies. Immunity following exposure to a disease is also a form of active immunity, where the body responds to an infection by generating its own immune response. Lastly, immunity from antibodies produced in response to a vaccine also describes active immunity, as the vaccination provokes the body’s immune system to create antibodies to respond to future exposures. Therefore, only the transfer of pre-formed antibodies aligns with the definition of passive immunity.