Low Humidity Found to Increase Risk of Flu

Investigators at Yale University believe that low humidity may explain a flu strain’s ability to remain active and easily transmitted, which may be connected to the immune system’s aptitude to fight against flu infection.

The research team examined the hypothesis with mice genetically modified to resist viral infections as humans do. The mice were housed in chambers at the same temperature, but at either low or normal humidity, and were then exposed to the influenza A virus.

According to a Yale press release, low humidity hindered the immune response of mice in three ways. It prevented cilia, hair-like structures in airway cells, responsible for removing viral particles and mucus. It also reduced the ability of airway cells to repair damage caused by the virus in the lungs. The third mechanism involved interferons, which are signaling proteins released by virus-infected cells to alert neighboring cells to the viral threat. In the low-humidity environment, the defense system found in these mice—and also in humans—failed. 

 "It's well known that where humidity drops, a spike in flu incidence and mortality occurs. If our findings in mice hold up in humans, our study provides a possible mechanism underlying this seasonal nature of flu disease," said study lead Akiko Iwasaki in a press release. 

Although it is not the only cause, humidity may be an important factor in preventing the influenza virus during the winter season. Increasing water vapor in the air with humidifiers at home, school, work, and even hospital environments is a potential strategy to reduce flu symptoms and speed recovery, the study authors said.