It is known that cold temperatures and decreased humidity promote the spread of the flu virus. However, experts have not fully understood the effect of low humidity on the immune system’s natural defenses against flu infection.
A team of researchers led by Professor Akiko Iwasaki set out to investigate using mice that were genetically modified to resist viral infection in the same way as humans. The mice were all housed at the same temperature, but were kept in chambers with either normal or low humidity. The mice were then exposed to the influenza A virus.
The study revealed that low humidity hindered the immune response of the mice in three critical ways. First, hair-like structures found in airway cells called cilia were prevented from removing viral particles and mucus. The low humidity also reduced the ability of airway cells to repair damage caused by the virus in the lungs.
Furthermore, signaling proteins that typically alert neighboring cells to a viral threat, known as interferons, were not activated by virus-infected cells in the low-humidity environment.
“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 Professor Iwasaki.
According to the researchers, while humidity is not the only contributor to flu outbreaks, it should be considered during the winter season. They noted that 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 is published in the journal Proceedings of the National Academy of Sciences.