Influenza virus infectiousness heavily affected by indoor humidity

High indoor humidity levels have been found to dramatically reduce the infectivity of influenza virus particles released by coughing.

A new study conducted by the U.S. National Institute for Occupational Safety and Health and the U.S. Centers for Disease Control and Prevention tested the effects of relative humidity on the capacity of the flu virus to re-infect cells, according to

The research, recently published in the journal PLoS One, found that an hour after being released in a room at a relative humidity of 23 percent or less, between 70 and 77 percent of viral particles retained their infectivity. When the humidity was increased to approximately 43 percent, only 14 percent were capable of infecting cells.

The majority of the inactivity occurred within the first 15 minutes of the initial release into high-humidity conditions. The study concluded that maintaining an indoor relative humidity level of approximately 40 percent can significantly reduce the infectiousness of the flu virus, according to

The study, and similar research, may explain why the flu virus tends to erupt when it grows cooler and drier during the winter months. A previously published study in the journal PLoS One examined the influenza virus while suspended in a solution that mimics human mucous.

In the study, researchers found that at low-humidity, the fake mucous dried and the viral particles thrived. When the humidity rose above 50 percent, the droplets partially evaporated and left a solution that was too salty for the virus to survive. When the humidity reached 100 percent, however, evaporation stopped completely and the mucus salinity provided an excellent environment for the virus. This could be a possible explain why the virus hits tropical regions during the rainy season, according to Scientific American.