Empty Child Syndrome

The "Empty Child" plague was a technological plague which spread around a part of London in 1941. The Ninth Doctor and Rose encountered the Empty Child and helped play a part in his cure.

History
Chula nanogenes, who had never previously encountered Humans infected a dying Human boy named Jamie caught in the Blitz, and thus created a so-called "Empty Child" with a gas mask for a face. The nanogenes also gave the child the standard abilities of Chula soldiers, specifically super-Human strength, telepathic abilities and the ability to communicate using other items. Unfortunately, the Empty Child still had a child-like mentality and escaped to search for its mother.

The Empty Child compulsively searched for his mother, and in doing so contaminated other Humans with the nanogenes. Those who were infected did likewise so that the nanogenes spread in a fashion similar to a virus.

All of the victims grew faces like gas masks and developed the same wounds as the original child, as well as the same compulsion. This plague was eventually stopped when the Doctor reunited the Empty Child with his mother and the nanogenes recognized the proper sequence for a Human in 1943 London. (DW: The Empty Child / The Doctor Dances)

Rose Tyler later described the victims as "gas-masked zombies" to Sarah Jane Smith when comparing things they have seen when traveling with the Doctor. (DW: School Reunion)

When given a gas mask, during Sontaran invasion of Earth the Tenth Doctor states "Are you my mummy?" a reference to these events (DW: The Poison Sky)