A live attenuated vaccine is a type of vaccine that uses a weakened form of a virus or bacterium to stimulate the immune system. This weakened pathogen is still alive but has been modified so it cannot cause disease in healthy individuals. By introducing this harmless version into the body, the immune system learns to recognize and fight the actual pathogen if it encounters it in the future. These vaccines are effective because they closely mimic a natural infection, leading to a strong and lasting immune response. Common examples of live attenuated vaccines include those for diseases like measles, mumps, and rubella.