Climate Change And The Flu: Warm Winters Followed By Severe Flu Seasons

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.

4 Responses to Climate Change And The Flu: Warm Winters Followed By Severe Flu Seasons

  1. Merrelyn Emery says:

    Obviously immunity is important and we have also seen migrations of West Nile (North) and Dengue (South) to previously unexposed populations. Migration of influenza strains as well as new mutations should be expected, ME

  2. From Peru says:

    According to CDC data, this outbreak is caused by the old, common seasonal influenza virus A/H3N2 and B . The Pandemic A/H1N1(2009) is instead rare(less than 3%of cases):


    Also, there are no cases of novel(i.e. possible pandemic-treathening swine or avian viruses) influenza strains this week. The situation is also very good on antiviral resistance (almost no cases of resistance to antivirals) and in the match between the circulating virus and the vaccine strains (all A2009/H1N1 analysed so far are vaccine-like and almost all A/H3N2 too, 2/3 of B viruses sampled are vaccine-like).

    The biological recipe is there for a very MILD influenza season, but deaths and outbreaks are at levels similar or above the 2009 pandemic levels. This is odd.

    Apparently, the mild flu seasons of last years (after the 2009-2010 pandemic) leaved a lot of people susceptible, so that even an average cold winter with a benign virus circulating caused a major outbreak.

    Frankly, this is a shame. Influenza is vaccine-preventable (and the almost perfect match between wild and vaccine virus makes this even more true than other years) , so the obvious reason for this emergency is that people do not get vaccinated.

    I have a question. For what damned reason people do not get vaccinated?! It is so difficult to act in a way to reduce future menaces?

    Wake up people! I get vaccinated every year. There are nearly 4 ininterrupted years that I dont’t catch even a common cold!

    If the society cannot do even one of the simplest actions to prevent illness and mortality (i.e. vaccinations), it is painfully clear that most people cannot even think in doing some modest sacrifices to prevent much more complicated problems, like climate change.

  3. Mulga Mumblebrain says:

    And isn’t it reassuring to see that scientists are once again investigating the transmissability between humans of H5N1 avian flu? Nothing could possibly go wrong, I’m sure.

  4. prokaryotes says:

    This is so big (climate state switch), people will not understand the profoundness in time. Not as long we put profits before safe guarding our habitat.