The Cyalax Virus was a specially engineered virus that replicated only in midichlorians and was quickly overwhelmed by a person's immune system if it could not locate midichlorians fast enough. This made it worthless as an intentional pandemic agent, but could be strategically used against Jedi and other Force-users. Viral research began thanks to funding by Empress Shira in 20 ABY, but it was eight years before the virus was perfected. Many scientists, including Sarra Vall, worked on the project at Shira's command.