In Isolation (1969) on Netflix

Four friends wanted to get away from it all for a birthday celebration in a remote country house, but when a mysterious injured man turns up on their doorstep telling tales of a city ravaged by a mysterious epidemic and the looters who have pursued him, the friends rally to help. As the night progresses, it becomes clear that all is not as it seems, plunging the friends into a battle for survival that challenges their deepest fears.