A new study links global warming to this year’s unusually severe flu season — a season which the Centers for Disease Contol officially dubbed an epidemic and which prompted New York Gov. Andrew Cuomo (D) to declare a state of emergency.
The scientists used data from the CDC to examine influenza and climate patterns going back to the 1997-1998 flu season. Previous studies have indicated that unusually warm winters, which will become more common in many areas as global warming continues, depress the spread of the flu. Ironically, this can leave populations more vulnerable to infection in the future as fewer people will develop immune system defenses.
As a result, the scientists found a pattern in which average-to-colder winters saw an unusually severe flu outbreak if they had been preceded by an unusually mild winter:
While the underlying causative dynamics of the severity and timing of influenza epidemics are multi-faceted, a primary contributing factor to the mildness of the 2011-12 season was likely the fact that the national meteorological winter of 2011-12 was the fourth warmest on record; several prior studies have shown that influenza transmissibility sharply decreases in warmer temperatures and/or high humidity.
In contrast to the 2011-12 season, the ongoing 2012-13 season is off to an unusually early and severe start, despite the fact that the national climate this past autumn was close to the seasonal average. Here we analyzed the weekly time series of confirmed influenza cases in the US from the 1997-98 influenza season to present. Our findings indicate that influenza epidemic severity and time of onset is significantly associated with the average winter temperature during the previous season, with severe and early influenza seasons being much more likely following a mild winter.
In the event of continued global warming, warmer than average winters are expected to occur more frequently, but variability in seasonal temperatures will of course remain, and average winters will still occur with regularity for some time to come. Our work suggests that mild influenza seasons during unusually warm winters are a harbinger of the likelihood of an unusually severe season to come. Hence, these 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.
“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,” Sherry Towers, the lead scientist on the team that did the study, told Science Daily. “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.”
Vaccinations remain the best tool for combating the flu, and the potential for unusually early flu seasons serves to highlight the importance of awareness even out of the flu season when vaccinations will not be at the top of the news cycle. Nor is the situation helped by the fact that 40 percent of America’s private sector workers, and 80 percent of low income workers, do not receive one day of paid sick leave from their employers.