Proc. Natl Acad. Sci. USA (2019)

Infection with respiratory viruses often increases during the colder and less-humid winter months; however, the host-intrinsic factors that contribute to this enhanced susceptibility have remained largely unclear. Iwasaki and colleagues, in the Proceedings of the National Academy of Sciences, report on infection with influenza A virus in mice kept under normal or low ambient humidity. Infection under low-humidity conditions results in worse symptoms, less-efficient epithelial repair, impaired mucociliary and innate immune cell–dependent clearance of the virus and reduced control of viral spreading. Furthermore, the expression of key interferon-regulated genes is also reduced under low relative humidity. The mechanism that underpins these diverse impairments seen under low humidity remains unknown but might be related to the induction of stress responses.