Cobb's injuries worsen, causing him to mutate and infect Doc. They do not generally mutate to cancerous growths, nor do they normally grow or spread. Vaccination has proved difficult as there are many viruses involved and they mutate rapidly. The virus did not mutate to a more lethal form. The gene could mutate, potentially causing unforeseen problems (as could any gene). H5N1 may mutate or reassort into a strain capable of efficient human-to-human transmission. Viral genomes mutate at a high rate. Since DNA repair is under genetic control, it can mutate. After some talk they mutate into dangerous beasts. In prostate cancer, the cells of these prostate glands mutate into cancer cells. However, some cells mutate in ways that escape these control mechanisms. This version is described to be a mutant instead of a mutate. These are caused by environmental factors that mutate one copy of the gene. The employees and Dr. Banner suddenly mutate into various Hulk creatures. As a result, a portion of the population will mutate into fish-like creatures.