Antiviral efficacy of different low doses of 222-nm far-UVC light. Typical fluorescent images of MDCK epithelial cells infected with influenza A virus (H1N1). The viruses were exposed in aerosolized form in the irradiation chamber to doses of 0, 0.8, 1.3 or 2.0 mJ/cm2 of 222-nm far-UVC light. Infected cells fluoresce green (blue = nuclear stain DAPI; green = Alexa Fluor-488 conjugated to anti-influenza A antibody). Images were acquired with a 40× objective.