The Dominion Phials contained the Dominion Virus, weaponized by the Styx to exterminate the Topsoilers, and its vaccine. They were given to the Rebecca Twins by their grandfather, the Old Styx, after testing on the virus in the Bunker was completed. The amount of virus contained in the Phial was enough to start a worldwide pandemic. After the Bunker was destroyed by Drake, and Sarah Jerome cast the Rebeccas into the Pore, recovery of the virus became a priority for the Styx. When they finally recovered the virus, it was useless to them, as Elliott had ingested the vaccine.