Study leader Sherry Towers, a research professor at Arizona State University, studied waves of influenza and climate patterns in the United States from the 1997-98 season to the present.
The research team said data from the Centers for Disease Control and Prevention indicate a pattern for both A and B strains: Warm winters were usually followed by heavy flu seasons.
"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," Towers said in a statement. "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."
The current flu season, began early and fiercely and followed a relatively light 2011-12 season, which saw the lowest peak of flu since tracking efforts went into effect, and coincided with the fourth warmest winter on record. Studies suggest flu transmission decreases in warm or humid conditions.
If global warming continues, warm winters will become more common, and the impact of flu will likely be more heavily felt, the study authors concluded.
The findings were published in PLOS Currents: Influenza.
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