Member of SG6, Lieutenant Fischer was sent on an undercover mission to P2X-885 to monitor the Ori activity on the planet. Whilst undercover, Fischer attended morning Prostration during which a Prior touched the top of his head. Unknown to him, this exchange had made him a carrier of the Prior plague.
Back on Earth, Fischer was given a clean bill of health and allowed to go off-base. Soon after the base personal fell ill with the Priors plague, and the SGC sent a team to extract Fischer, who was attending a speech by General George Hammond. Fortunately, General Hammond had not been infected, however Fischer was identified as the carrier and quarantined.
Fischer as the carrier, was immune to the effects of the plague.