In recent years a number of authors have conducted systematic reviews of the effectiveness of strategies to prevent and control the spread of respiratory viruses.1,–,4 The work is important because respiratory virus infections cause considerable morbidity and mortality, especially among children in developing countries and older people, and account for much time away from work and school. There is persuasive evidence from laboratory and epidemiological studies that colds are spread mainly via large droplets (1–5 µm), which …