Final answer:
Live attenuated vaccines contain a modified pathogen that does not cause disease in healthy individuals. They work by provoking an immune response through a weakened form of the virus, which has been altered to reduce its virulence.
Step-by-step explanation:
The type of vaccine that contains a modified organism, which is not capable of causing disease in healthy individuals, is known as a live attenuated vaccine. Live attenuated vaccines are created by weakening the wild-type virus or pathogen, enabling the vaccine to provoke an adaptive immune response without causing the actual disease. The process involves growing the virus in laboratory conditions that are different from its natural environment, which leads to mutations that diminish its disease-causing capability.
However, there is a risk with live vaccines, as they can potentially revert to a virulent form through back mutations. An example of this occurring is the 2007 polio epidemic in Nigeria, caused by mutations in the polio vaccine. Nevertheless, vaccinations remain a highly effective method for preventing viral infections, as they induce immunity without causing the diseases they protect against.