Live attenuated vaccines are made from viruses or bacteria that have been weakened, so they cannot cause disease in healthy individuals. These vaccines stimulate the immune system to recognize and fight the actual pathogen if encountered in the future. Examples include vaccines for diseases like measles, mumps, and rubella. Because they closely mimic a natural infection, live attenuated vaccines often provide long-lasting immunity with fewer doses. However, they may not be suitable for people with weakened immune systems, such as those undergoing treatment for cancer or living with HIV.