NFS plague

The NFS plague, or Neurotransmitter Failure Syndrome, was a particularly virulent infection that had engulfed the Border Worlds in the two-thousand years following the Great Catastrophe.

The symptoms of the disease caught its victims by surprise and were very difficult to treat. Sufferers endured a constant buzzing sound in their heads, along with difficulty speaking. Those less-fortunate to survive were described as having their bodies physically fall apart. There was no cure for the disease and only a heavy treatment of antibiotics and other drugs could keep the disease from progressing beyond a certain point. (BFDE: The Healers)

The Daleks had developed a cure for the NFS Plague; a substance called "Variant 7." The drug was a success, freeing the plague victims of years of suffering. However, it was only administered in complex "healing zones" on geo-formed worlds. (BFDE: The Demons)