The G-virus is similer to the T-virus it was made by Jacobs arch foe William Birkin after William shot Jacob nothing happend he's immortal Jacob injected the G-virus into his body in order to transform into a monster of fire he killed William his next vitume is Annette he's getting revenge cause she betryed him he hates Umbrella. While in the underground lab Claire gave Jacob the papers for the G-virus antidot to save Sherry and her Jacob can't fail the promise he made to his parents he gave them the antidot after escaping the underground lab