Variant 7

Variant 7 was a cure created by the Daleks for use against the NFS plague that had engulfed the inhabitants of the galaxy.

It was part of an elaborate plan by the Dalek Empire to boost their numbers after the Great Catastrophe. Variant 7 was provided to the individuals suffering from the plague which contained extra DNA embedded within it which remained dormant in the body. Once it was exposed to a certain form of radiation, this added DNA converts the host into a new Dalek allowing for the Empire to create a massive army. (BFA: Dalek Empire III: The Future)