It has been considered unlikely that a person in a vegetative state will regain consciousness beyond 12 months after a traumatic brain injury or 3 months after an anoxic or hemorrhagic injury.
However, ongoing improvements in both research methodology and medical intervention may be changing this way of thinking. A recent study of long-term vegetative state patients showed that 20% recovered responsiveness after 12 months, and 12% of those further progressed to regain consciousness. This recovery was associated strongly with younger age and occurred more often in traumatic brain injury, rather than anoxic or hemorrhagic.
Unfortunately, although responsiveness and consciousness can be recovered in some cases of vegetative state, it is also associated with severe functional impairments. Still, that the recovery rates were unexpectedly high in this study is an issue with ethical implications that should be addressed by medical and legal professionals.
Estraneo A, Moretta P, Loreto V, et al. Late recovery after traumatic, anoxic, or hemorrhagic long-lasting vegetative state. Neurology. (July 2010).