Warmer than average winters could result in more severe flu epidemics, according to research published Monday in PLOS Currents: Influenza.

The study mathematically analyzed climate patterns and cases of influenza in the U.S. from 1997 to the present. Though mild winters tended to reduce the spread of influenza, the following year often brought an early and severe outbreak because of lessened immunity.

"It appears that fewer people contract influenza during warm winters, and this causes a major portion of the population to remain vulnerable into the next season, causing an early and strong emergence," said Sherry Towers of Arizona State University, the lead author of the study.

"And when a flu season begins exceptionally early, much of the population has not had a chance to get vaccinated, potentially making that flu season even worse."

If global temperatures continue to rise, warm winters are expected to occur more frequently, resulting in a higher risk of severe flu epidemics.

But the authors of the study noted their findings could also help prevent flu outbreaks by encouraging people to receive vaccinations following a mild winter.

"[T]hese findings could guide improved prevention efforts, including progressive vaccination programs after a mild winter to achieve high vaccination coverage well in advance of the next influenza season," Towers and her colleagues said.

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[Sick woman taking her temperature via Shutterstock]