New research data show that low humidity and low temperatures promote the spread of the influenza A virus. Even small weather differences between regions can influence the severity of the flu season. Details of the study are also explained by first author Dr. Elisabeth Pfrommer in the latest episode of „Mikroben im Visier“, the podcast of the research alliance Leibniz INFECTIONS.

The spread of seasonal influenza waves in Germany is closely linked to weather conditions. Researchers from the Research Center Borstel, Leibniz Lung Center and other Leibniz institutions have found that the transmission of the influenza A virus is facilitated by cold and dry air. Even minor regional differences in temperature and humidity can affect the severity of the flu season. The study was published in the scientific journal Aerobiologia and was conducted as part of the research alliance Leibniz INFECTIONS.

Weather as a driver of virus spread

For the study, researchers analyzed epidemiological data on influenza cases between 2010 and 2018 from the Robert Koch Institute and combined it with weather data from the German Weather Service. A clear geographical difference emerged: In south-eastern regions of Germany, flu waves were more intense than in the north-west — a pattern closely linked to levels of dryness and cold.

“Our results demonstrate that even in a country like Germany, which is relatively climatically homogeneous, there are measurable differences in regional weather that affect the transmission of influenza,” says Dr Elisabeth Pfrommer, the study’s first author. “In particular, low absolute humidity increases the stability and transmissibility of influenza viruses in the air.”

Big cities as infection hotspots

The study also identified major cities such as Berlin, Hamburg, Munich, and Cologne as the starting points of flu outbreaks. These cities have a higher population density, and many people spend time indoors during winter, creating conditions that facilitate virus transmission.

“Cities act as drivers of the flu season. From here, infections spread to surrounding regions,” explains Professor Thomas Gutsmann, leader of the study at the Research Center Borstel, Leibniz Lung Center.

In addition to meteorological influences, social factors also play a role: indoor heating reduces relative humidity, which increases both the survival of viruses and the susceptibility of human mucous membranes.

Implications for infection research and prevention

The findings are relevant not only for influenza research, but also for other respiratory diseases, such as COVID-19. Differences in temperature and humidity influence not only virus stability, but also how quickly infections spread within cities and districts.

The authors advocate integrating climate data more strongly into epidemiological models in the future. In addition, the indoor climate should be considered in prevention strategies, for example, through air humidification or controlled ventilation in public buildings.

New podcast episode: Airborne transmission of viruses and seasonal flu waves

Further Details about the new study, as well as information on the spread of viruses through the air in general, can be found in the latest episode of the podcast “Mikroben im Visier.” This episode explains aerosols and droplets, why children spread fewer viruses through the air than many people think, and why winter favours infections. The podcast is hosted by Dr Elisabeth Pfrommer and Dr Christian Nehls. Their guest is pediatric pulmonologist Professor Dr Folke Brinkmann from the University of Lübeck.

Source:

Pfrommer, E., Gabriel, G., Schaible, U.E., Gutsmann, T., Schepanski, K. (2025): Transmission of Influenza is Driven by Weather Conditions in Germany. Aerobiologia. https://doi.org/10.1007/s10453-025-09875-9