A recent article from theJournal of Indoor Environmental Qualityhas found that the survival of the influenza virus in the air and on surfaces is modulated by moisture levels, having the lowest levels in the range of 40-60% RH. Its studies have shown that indoor humidification will increase AH and RH to levels that reduce the virus, and thus humidifiers may be vital in reducing the survival of the flu in the home. For more on this, read “Effects of Humidification on Influenza Virus Survival in Rooms Conditioned with Radiant Heating and Forced Air.” 

Source: http://blogs.healthyheating.com