A live attenuated virus is a weakened form of a virus that can still replicate but does not cause disease in healthy individuals. This type of virus is often used in vaccines to stimulate the immune system without causing illness. By introducing a harmless version of the virus, the body learns to recognize and fight the actual virus if exposed in the future. These vaccines, such as those for measles, mumps, and rubella, help build immunity by prompting the body to produce antibodies. Live attenuated virus vaccines are generally effective and provide long-lasting protection, making them a crucial tool in public health.