What is the main characteristic of a live vaccine?

A live vaccine is characterized by being prepared from live microorganisms or viruses that have been attenuated, meaning they have been weakened so they cannot cause disease in healthy individuals. These vaccines are designed to stimulate a robust immune response, mimicking the natural infection process without causing the illness itself. This can lead to long-lasting immunity with typically fewer doses required compared to inactivated or killed vaccines.

Unlike killed vaccines, which contain dead pathogens and cannot replicate, live vaccines leverage the ability of live microorganisms to invoke a strong and comprehensive immune response that includes both humoral (antibody-mediated) and cellular immunity. They often require careful handling and specific storage conditions, commonly needing refrigeration to maintain their viability, but they are not limited to higher dose requirements in the same way some inactivated vaccines might be.