Apocalypse domani (1980)

It starts off in Vietnam where John Saxon gets bitten by P.O.W. John Morghen who has been infected with some sort of cannibal virus. A few decades later in Atlanta, Georgia, Saxon wakes up from a nightmare flashback of what actually happened back in 'Nam. Saxon then receives a call from Morghen asking him if he wants to go out for a drink but Saxon refuses remembering the incident in 'Nam. Morghen has turned into a cannibal and is soon on the run after biting into a woman's neck. He barricades himself in a department store and shoots some folks with a shotgun. The cannibal virus spreads and soon Saxon joins veterans Morghen and Tony King along with some others to wreak some havoc.