The correct answer is attenuated live vaccine.
Attenuated live vaccines are vaccines that use a weakened or attenuated form of the viruses or bacteria that causes a disease. Viruses or bacteria are given in a relatively small dose to replicate in the vaccinated person and to stimulate an immune response. They create a strong and long-lasting immune response but the limiting factor is that there is a possibility for a virus to revert to a form which is capable of causing disease.
