THURSDAY, Feb. 20, 2020 (HealthDay News) -- Climate change, and the sudden weather changes it brings, could fuel future flu epidemics, researchers warn in a new report.

They used historical data to assess how major weather swings in the fall months could affect flu season in highly populated areas of the United States, mainland China, Italy and France.

Specifically, the researchers examined weather patterns and average temperatures from Jan. 1, 1997, to Feb. 28, 2018, over more than 7,700 days. They also analyzed influenza data from the four countries over the same time period.

Previous research suggested that low temperatures and low humidity in the winter create favorable conditions for flu virus transmission. However, the 2017-2018 flu season was one of warmest on record, and also one of the deadliest.

During the 2017-2018 flu season, extreme swings in autumn weather "kick-started" the flu, resulting in flu cases early in the season that snowballed in highly populated areas, according to the study authors.

"The historical flu data from different parts of the world showed that the spread of flu epidemic has been more closely tied to rapid weather variability, implying that the lapsed human immune system in winter caused by rapidly changing weather makes a person more susceptible to flu virus," explained lead researcher Zhaohua Wu, an associate professor in the Department of Earth, Ocean and Atmospheric Science at Florida State University.

These findings suggest that rapid weather changes associated with climate change will increase the risk of flu epidemics in densely populated areas. For example, Europe could have a 50% increase in flu-related deaths, according to the researchers.

They said that learning more about major weather swings associated with climate change may prove important in predicting future flu season threats.

"The autumn rapid weather variability and its characteristic change in a warming climate may serve not only as a skillful predictor for spread of flu in the following season but also a good estimator of future flu risk," Wu said in a university news release. "Including this factor in flu-spread models may lead to significantly improved predictions of flu epidemic."

The study was published recently in the journal Environmental Research Letters.

More information

The U.S. Centers for Disease Control and Prevention has more on the flu.