Researchers from Yale have pointed out low humidity as a major reason why there is a higher likelihood of people getting sick or dying from the flu during winter months.
It is known that low humidity and cold temperatures promote flu virus transmission. However, decreased humidity effect on the body’s immune system’s defenses against flu infection is not quite well understood.
The Yale research team that was led by Akiko Iwasaki explored this question. They did this with the use of genetically modified mice for them to resist the viral infections just like humans do. The mice were reserved in chambers at same temperatures with either normal or low humidity. The mice were then exposed to the influenza A virus.
The team discovered that low humidity hindered immune responses of the mice in 3 ways:
- It prevented cilia, hair-like structures in airways cells, from removing mucus and viral particles.
- It reduced the airway cells’ ability to repair the damaged that the virus caused in the lungs.
- The 3rd mechanism, interferons were involved, or the signaling of proteins that were released by cells which were virus-infected so as to alert the neighboring cells of the viral threat. In an environment with low humidity, the innate immune defense system failed.
This study offers details as to why the flu prevails when the air is dry. According to Iwasaki, when there is a drop in humidity, there is a spike in flu incidences and mortality. If their discovery in mice holds up in humans, the study will provide a possible mechanism concerning this seasonal nature of the flu disease.
The researchers put emphasis on the fact that humidity is not the only factor present in flu outbreaks. It is, however, an important factor which should be considered during winter seasons. A potential technique to reduce symptoms of flu and speed up recovery would be to increase water vapor in the air using humidifiers at work, school, home and hospital environments.
The study got published in the Proceedings of the National Academy of Sciences (PNAS).
Other authors include Eriko Kudo, Laura Yockey, Eric Song, Tasfia Rakib, Robert Homer and Patrick Wong.
This study was supported partly by the Howard Hughes Medical Institute, a gift from the Naito Foundation, the Condair Group and National Institutes of Health grants.
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- Yale University. (2019, May 13). Flu virus’ best friend: Low humidity. https://news.yale.edu/2019/05/13/flu-virus-best-friend-low-humidity