Yale researchers have pinpointed a key reason why the immune system defence mechanisms are likely to deteriorate from viruses during flu season, and this is because of: low humidity.
During flu season, we know that the immune system defence mechanisms are relatively weak due to changing weather, however the effect of decreased humidity may now also be a playing factor.
Published in Proceedings of the National Academy of Sciences (PNAS), while experts know that cold temperatures and low humidity promote transmission of the flu virus, less is understood about the effect of decreased humidity on the immune system’s defences against flu infection.
Immune system defence mechanisms
The Yale research team, led by Akiko Iwasaki, the Waldemar Von Zedtwitz Professor of Immunobiology, explored the question using mice genetically modified to resist viral infection as humans do. The mice were all housed in chambers at the same temperature, but with either low or normal humidity, they were then exposed to the influenza A virus.
The researchers discovered that low humidity hindered the immune response of the animals in three ways. It prevented cilia, which are hair-like structures in airways cells, from 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, or signalling proteins released by virus-infected cells to alert neighbouring cells to the viral threat. In the low-humidity environment, this innate immune defence system failed.
Humidity is indeed a factor of flu outbreaks
The study offers insight into why the flu is more prevalent when the air is dry. Iwasaki explains: “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.”
While the researchers emphasised that humidity is not the only factor in flu outbreaks, it is an important one that should be considered during the winter flu season.
According to the researchers, increasing water vapour in the air with humidifiers at home, school, work, and even hospital environments is a potential strategy to reduce flu symptoms and speed recovery.