An apparatus is disclosed for practicing a method of treating viruses in the nasal mucosa. Vapor is generated, heated and delivered to the nasal mucosa in intermittent bursts, timed to coincide with inhalation. Control circuits are provided to maintain the temperature of the vapor at the point of delivery at a level greater than that necessary to kill viruses in the nasal mucosa. Timing circuits can synchronize the vapor delivery with a breathing cycle with heated vapor being supplied during inhalation and blocked during exhalation. Other circuits terminate operation when liquid is insufficient or after a predetermined timed interval.