Final answer:
A modified live vaccine uses an attenuated strain of a virus or other pathogen to stimulate an immune response without causing the disease. These vaccines are more effective than killed vaccines, but they come with the risk of the pathogen reverting to its virulent form. Handling and storage of these vaccines require careful consideration due to their nature.
Step-by-step explanation:
A modified live vaccine is a type of immunization that uses a weakened (attenuated) form of the living microorganism. The process of attenuation involves reducing the virulence of a 'wild-type' virus, which means it can stimulate an immune response without causing the disease that the full-virulence pathogen would cause. The goal is to induce protective immunity, utilizing the capacity of the live microorganisms to replicate and thereby activate both the cellular and humoral branches of the immune system for long-lasting protection.
Despite the benefits, there is a significant danger associated with live vaccines. The attenuated pathogens have the potential to revert to their disease-causing form through back mutations, which can lead to outbreaks of disease. Additionally, for immunocompromised individuals, the live vaccine itself can sometimes cause disease symptoms.
Live vaccines also require careful handling due to challenges in long-term storage and transport. Successful examples of live attenuated vaccines include those for diseases like measles, mumps, rubella, and polio. These vaccines have had a profound effect on reducing the incidence of these diseases globally.