A disadvantage of using a live microbe in a vaccine is it can conceivably mutate back to a virulent strain.

Question

Quizplus · Accepted Answer

This is true. Live attenuated vaccines use weakened forms of the pathogen to trigger an immune response. While the weakened form should not be able to cause disease in a healthy person, there is a small risk of the microbe mutating back to a virulent strain and causing disease. This risk is generally small and outweighed by the benefits of vaccination, but it is a potential disadvantage of using live microbes in vaccines.

A Disadvantage of Using a Live Microbe in a Vaccine