Strangerville Mystery Problem

Actually I don't know if I am completing correctly or if it is some kind of bug, which I have had many in last month unfortunately. Anyway, I am ready to fight Mother Plant, have vaccinated 3 friends and recruited them; when I try to lead them down hallway with spores, all 3 vaccinated sims start coughing, return to clear area and pass out. It won't let me vaccinate them again and they can't get past first hallway to help me fight mother plant.  Am I doing something wrong?