Live attenuated vaccines are a type of vaccine that contains a weakened form of the virus or bacteria that causes a disease. These vaccines stimulate the immune system to recognize and fight the pathogen without causing the actual disease. Because they closely mimic a natural infection, they often provide strong and long-lasting immunity. Examples of live attenuated vaccines include those for measles, mumps, rubella, and yellow fever. While they are generally safe and effective, they may not be suitable for individuals with weakened immune systems, as there is a small risk of the weakened pathogen causing illness in these cases.