Unlike Invictus, Provictus did not intrinsically affect behaviour nor cause death and could be used as a vaccine against the original strain. It read the infected's mind and uploaded their data to the Data Core, which was also able to insert thoughts. (AUDIO: "Invasion: Kill")
Dr Larsen said that the intended use of Provictus was to infiltrate terrorist cells. A minister arranged for an outbreak of Invictus as a way to get the population of Cardiff inoculated with Provictus as a means of surveillance and mind-control.
After Dr Godalming inoculated Cardiff, the minister told her to inoculate the whole of the United Kingdom. However, Jack Harkness activated a trojan horse hidden within his personal data to deactivate both strains of the virus. A real vaccine was created and Heights were defeated, with Jack telling the minister that he would be going to prison. (AUDIO: "Invasion: Kill")