how does attenuation ensure safe and effective vaccination?...

Question: 

how does attenuation ensure safe and effective vaccination?

Answer: 

According to the CDC: "Live attenuated vaccines fight viruses and bacteria. These vaccines contain a version of the living virus or bacteria that has been weakened so that it does not cause serious disease in people with healthy immune systems. Because live, attenuated vaccines are the closest thing to a natural infection, they are good teachers for the immune system. Examples of live, attenuated vaccines include measles, mumps, and rubella vaccine (MMR) and varicella (chickenpox) vaccine." Live attenuated vaccines can result in lifelong immunity with just one or two doses.

ImmunizeBC Nurse