What type of vaccines are composed of live, attenuated organisms?

Live vaccines consist of live, attenuated organisms that have been modified to reduce their virulence while still eliciting a strong immune response. These vaccines are effective in stimulating both humoral and cellular immunity, enabling the body to recognize and respond to the actual pathogen if encountered in the future. The concept of using a weakened form of a pathogen provides a robust, long-lasting immunity, as the immune system can produce a response similar to that triggered by a natural infection without causing the disease itself.

In contrast, subunit vaccines are made from pieces of the pathogen, such as proteins or sugars, which do not include any live components. Inactivated vaccines are composed of pathogens that have been killed or inactivated, and do not retain the capability to replicate or cause disease. Toxoid vaccines contain inactivated toxins produced by the pathogen rather than the pathogen itself. Each of these types of vaccines has its specific mechanisms and uses, but the defining characteristic of live vaccines is their use of live, albeit weakened, organisms to provoke an immune response.