The PRIOR2 virus, also known as the PRIOR2 plague, Prior plague, or Ori plague, is a sickness that spreads through contact between people and is triggered by Priors of the Ori. It is used by the Ori as a biological weapon, and is most likely deployed whenever a planet hesitates in declaring their acceptance of Origin. (SG1: "The Powers That Be")
It is a multi-resistant virus that spreads through direct or indirect contact. Earth initially had no cure for this very lethal sickness, but due to the actions of Orlin the planet is now protected against further threats. The ascended Ancients have the ability to cure this sickness, but because of their non-interference policy, they refuse to act. People who are near ascension can use their healing power to cure the plague, though not on a scale anywhere near as large as the ascended could. Goa'uld Healing Devices only temporarily relieve the symptoms of the plague, and cannot cure it. (SG1: "The Fourth Horseman, Part 1", "The Fourth Horseman, Part 2")
- Main article: Ori plague outbreak on Earth
A Prior used this on the planet P8X-412 to get the residents' devotion and obedience to the Ori (which they ultimately got due to the effectiveness of the plague). They also infected Lt. Fischer with this plague as a carrier to Earth. The plague then rapidly spread to nearly every inhabited location on Earth, including both American continents, Europe and Africa. With the help of Orlin's regained memory from the Ancients and that of the Prior Gerak, the plague was stopped. Gerak removed the virus from Stargate Command, resulting in his own agonizing death, and Orlin's work helped the doctors under Carolyn Lam to develop an antivirus that effectively stopped the plague. (SG1: "The Powers That Be", "The Fourth Horseman, Part 1", "The Fourth Horseman, Part 2") SG-1 later spread the cure to the infected worlds (and even to an alternate reality in desperate need of a cure (SG1: "Ripple Effect"). The Priors stopped using their biological weapon after learning that it was no longer effective.
Daniel Jackson hypothesized that the Ori plague was the one the Ancients were suffering from when they left for Pegasus. He was partially correct as while the plague was not the same one that afflicted the Ancients, it was caused by the Ori through the Doci instructing the Ancient Amara to create it. Ironically, this act made the Ori the harbingers of their own doom, as it was this action that led to the creation of their future enemies: the Tau'ri. (SG1: "Frozen", "Transitions", "The Powers That Be") (SGA: "Rising")