Final answer:
A live attenuated vaccine is prepared from live microorganisms that have lost their virulence but retained their ability to induce protective immunity. These vaccines stimulate a comprehensive immune response, leading to long-lasting immunity.
Step-by-step explanation:
A live attenuated vaccine is prepared from live microorganisms that have lost their virulence but retained their ability to induce protective immunity. These vaccines expose an individual to a weakened strain of a pathogen, which establishes a subclinical infection, activating the adaptive immune defenses. The pathogens are attenuated through genetic manipulation or long-term culturing in an unnatural host or environment.
Live attenuated vaccines stimulate a comprehensive immune response, activating both cellular and humoral immunity, and stimulate the development of long-lasting immunity. They can even lead to the natural transmission of the attenuated pathogen, causing others to also develop an active, subclinical infection and activate their immune defenses.